说明：为书写方便起见，后文将SurfaceFlinger简写为SF。

private final voidhandleLaunchActivity(ActivityRecord r, Intent customIntent) {

       //①performLaunchActivity返回一个Activity

       Activitya = performLaunchActivity(r, customIntent);

        if(a != null) {

           r.createdConfig = new Configuration(mConfiguration);

           Bundle oldState = r.state;

          //②调用handleResumeActivity

           handleResumeActivity(r.token, false, r.isForward);

      ......

private final ActivityperformLaunchActivity(ActivityRecord r,

Intent customIntent) {

       ActivityInfo aInfo = r.activityInfo;

        ......//完成一些准备工作

      //Activity定义在Activity.java中

       Activity activity = null;

           java.lang.ClassLoader cl = r.packageInfo.getClassLoader();

     mInstrumentation为Instrumentation类型，源文件为Instrumentation.java。

     它在newActivity函数中根据Activity的类名通过Java反射机制来创建对应的Activity，

     这个函数比较复杂，待会我们再分析它。

           activity = mInstrumentation.newActivity(

                    cl,component.getClassName(), r.intent);

            r.intent.setExtrasClassLoader(cl);

           if (r.state != null) {

               r.state.setClassLoader(cl);

        }catch (Exception e) {

            ......

           Application app =

             r.packageInfo.makeApplication(false,mInstrumentation);

            if (activity != null) {

               //在Activity中getContext函数返回的就是这个ContextImpl类型的对象

               ContextImpl appContext = new ContextImpl();

               ......

              //下面这个函数会调用Activity的onCreate函数

               mInstrumentation.callActivityOnCreate(activity, r.state);

                ......

       return activity;

final void handleResumeActivity(IBinder token,boolean clearHide,

boolean isForward) {

boolean willBeVisible = !a.mStartedActivity;

if (r.window == null && !a.mFinished&& willBeVisible) {

      r.window= r.activity.getWindow();

      //①获得一个View对象

      Viewdecor = r.window.getDecorView();

     decor.setVisibility(View.INVISIBLE);

      //②获得ViewManager对象

      ViewManagerwm = a.getWindowManager();

      ......

      //③把刚才的decor对象加入到ViewManager中

       wm.addView(decor,l);

         ......//其他处理

public void setContentView(View view) {

//getWindow返回的是什么呢？一起来看看。

 getWindow().setContentView(view);

public Window getWindow() {

  returnmWindow; //返回一个类型为Window的mWindow，它是什么？

activity = mInstrumentation.newActivity(

                    cl,component.getClassName(), r.intent);

public Activity newActivity(Class<?>clazz, Context context,

           IBinder token, Application application, Intent intent,

            ActivityInfo info, CharSequencetitle, Activity parent,

String id,Object lastNonConfigurationInstance)

throws InstantiationException, IllegalAccessException{

Activity activity = (Activity)clazz.newInstance();

       ActivityThread aThread = null;

        //关键函数attach!!

       activity.attach(context, aThread, this, token, application, intent,

info, title,parent, id, lastNonConfigurationInstance,

new Configuration());

       return activity;

final void attach(Context context,ActivityThread aThread,

           Instrumentation instr, IBinder token, int ident,

           Application application, Intent intent, ActivityInfo info,

           CharSequence title, Activity parent, String id,

           Object lastNonConfigurationInstance,

           HashMap<String,Object> lastNonConfigurationChildInstances,

           Configuration config) {

        ......

        //利用PolicyManager来创建Window对象

       mWindow = PolicyManager.makeNewWindow(this);

       mWindow.setCallback(this);

        ......

        //创建WindowManager对象

       mWindow.setWindowManager(null, mToken, mComponent.flattenToString());

        if(mParent != null) {

           mWindow.setContainer(mParent.getWindow());

       //保存这个WindowManager对象

       mWindowManager = mWindow.getWindowManager();

       mCurrentConfig = config;

注意，上面路径中的灰色目录phone是针对智能手机这种小屏幕的；另外还有一个平级的目录叫mid，是针对Mid设备的。mid目录的代码比较少，可能目前还没有开发完毕。

public final class PolicyManager {

   private static final String POLICY_IMPL_CLASS_NAME =

       "com.android.internal.policy.impl.Policy";

   private static final IPolicy sPolicy;

    static{

           Class policyClass = Class.forName(POLICY_IMPL_CLASS_NAME);

           //创建Policy对象

           sPolicy = (IPolicy)policyClass.newInstance();

        }catch (ClassNotFoundException ex) {

            ......

    private PolicyManager() {}

    //通过Policy对象的makeNewWindow创建一个Window

    publicstatic Window makeNewWindow(Context context) {

       return sPolicy.makeNewWindow(context);

   ......

public class Policy implements IPolicy {

   private static final String TAG = "PhonePolicy";

   private static final String[] preload_classes = {

       "com.android.internal.policy.impl.PhoneLayoutInflater",

       "com.android.internal.policy.impl.PhoneWindow",

       "com.android.internal.policy.impl.PhoneWindow$1",

       "com.android.internal.policy.impl.PhoneWindow$ContextMenuCallback",

       "com.android.internal.policy.impl.PhoneWindow$DecorView",

       "com.android.internal.policy.impl.PhoneWindow$PanelFeatureState",

"com.android.internal.policy.impl.PhoneWindow$PanelFeatureState$SavedState",

    static{

        //加载所有的类

       for (String s : preload_classes) {

               Class.forName(s);

           } catch (ClassNotFoundException ex) {

               ......

public PhoneWindow makeNewWindow(Contextcontext) {

        //makeNewWindow返回的是PhoneWindow对象

       return new PhoneWindow(context);

    ......

mWindow = PolicyManager.makeNewWindow(this);

  ......//创建mWindow对象

   //调用mWindow的setWindowManager函数

mWindow.setWindowManager(null, mToken,mComponent.flattenToString());

   .....

public class PhoneWindow extends Windowimplements MenuBuilder.Callback

public void setWindowManager(WindowManagerwm,IBinder appToken, String appName) {     //注意，传入的wm值为null

       mAppToken = appToken;

       mAppName = appName;

        if(wm == null) {

          //如果wm为空的话，则创建WindowManagerImpl对象

           wm = WindowManagerImpl.getDefault();

       //mWindowManager是一个LocalWindowManager

       mWindowManager = new LocalWindowManager(wm);

private class LocalWindowManager implementsWindowManager {

       LocalWindowManager(WindowManager wm) {

           mWindowManager = wm;//还好，只是简单地保存了传入的wm参数

           mDefaultDisplay = mContext.getResources().getDefaultDisplay(

                   mWindowManager.getDefaultDisplay());

    ......

public class WindowManagerImpl implementsWindowManager {

......

public static WindowManagerImpl getDefault()

     return mWindowManager; //返回的就是WindowManagerImpl对象

private static WindowManagerImpl mWindowManager= new WindowManagerImpl();

public void setContentView(View view) {

       getWindow().setContentView(view);//getWindow返回的是PhoneWindow

public void setContentView(View view) {

   //调用另一个setContentView

   setContentView(view,

new ViewGroup.LayoutParams(MATCH_PARENT,MATCH_PARENT));

public void setContentView(View view,ViewGroup.LayoutParams params) {

   //mContentParent为ViewGroup类型，它的初值为null

     if(mContentParent == null) {

           installDecor();

     }else {

           mContentParent.removeAllViews();

    //把view加入到ViewGroup中

    mContentParent.addView(view, params);

     ......

这里采用的是23种设计模式中的Composite模式，它是UI编程中常用的模式之一。

private void installDecor() {

    if (mDecor == null) {

     //创建mDecor，它为DecorView类型，从FrameLayout派生

     mDecor= generateDecor();

            ......

  if(mContentParent == null) {

     //得到这个mContentParent

mContentParent = generateLayout(mDecor);

//创建标题栏

    mTitleView= (TextView)findViewById(com.android.internal.R.id.title);

......

protected ViewGroup generateLayout(DecorViewdecor){

  ......

  intlayoutResource;

  intfeatures = getLocalFeatures();

  if((features & ((1 << FEATURE_LEFT_ICON) |(1 <<FEATURE_RIGHT_ICON))) != 0) {

      if(mIsFloating) {

      //根据情况取得对应标题栏的资源id

     layoutResource =  com.android.internal.R.layout.dialog_title_icons;

       ......

  mDecor.startChanging();

 View in =mLayoutInflater.inflate(layoutResource, null);

 //加入标题栏

 decor.addView(in,new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT));

ID_ANDROID_CONTENT的值为”com.android.internal.R.id.content”

     这个contentParent由findViewById返回，实际上就是mDecorView的一部分。

   ViewGroupcontentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);

   ......

   mDecor.finishChanging();

   returncontentParent;

public View findViewById(int id) {

  //getDecorView将返回mDecorView,所以contentParent确实是DecorView的一部分

   returngetDecorView().findViewById(id);

注意，这里使用了设计模式中的Decorator（装饰）模式，它也是UI编程中常用的模式之一。

final void handleResumeActivity(IBinder token,boolean clearHide,

boolean isForward) {

 booleanwillBeVisible = !a.mStartedActivity;

......

if (r.window == null && !a.mFinished&& willBeVisible) {

     r.window= r.activity.getWindow();

    //①获得一个View对象。现在知道这个view就是DecorView

   Viewdecor = r.window.getDecorView();

   decor.setVisibility(View.INVISIBLE);

  //②获得ViewManager对象,这个wm就是LocalWindowManager

  ViewManagerwm = a.getWindowManager();

  WindowManager.LayoutParamsl = r.window.getAttributes();

  a.mDecor= decor;

  l.type =WindowManager.LayoutParams.TYPE_BASE_APPLICATION;

  if(a.mVisibleFromClient) {

       a.mWindowAdded= true;

       //③把刚才的decor对象加入到ViewManager中

      wm.addView(decor,l);

......//其他处理

由于代码比较长，跳转关系也很多，在分析代码时，请读者把握流程，在大脑中建立一个代码分析的堆栈。

wm.addView(decor, l);//wm类型实际是LocalWindowManager

public final void addView(View view,ViewGroup.LayoutParams params) {

 WindowManager.LayoutParams wp =(WindowManager.LayoutParams)params;

 CharSequence curTitle = wp.getTitle();

 ...... //做一些操作，可以不管它

//还记得前面提到过的Proxy模式吗？mWindowManager对象实际上是WindowManagerImpl类型

mWindowManager.addView(view, params);

private void addView(View view,ViewGroup.LayoutParams params, boolean nest)

  ViewRootroot; //ViewRoot，幕后的主角终于登场了！

  synchronized(this) {

  //①创建ViewRoot

  root =new ViewRoot(view.getContext());

  root.mAddNesting = 1;

  view.setLayoutParams(wparams);

  if(mViews == null) {

      index = 1;

      mViews = new View[1];

      mRoots= new ViewRoot[1];

     mParams = new WindowManager.LayoutParams[1];

   } else{

     ......

   index--;

   mViews[index]= view;

   mRoots[index]= root;//保存这个root

   mParams[index]= wparams;

//②setView,其中view是刚才我们介绍的DecorView

  root.setView(view,wparams, panelParentView);//

public final class ViewRoot extends Handlerimplements ViewParent,

       View.AttachInfo.Callbacks //从Handler类派生

private final Surface mSurface = new Surface();//这里创建了一个Surface对象

final W mWindow; //这个是什么？

View mView;

static class W extends IWindow.Stub

public ViewRoot(Context context) {

       super();

       // getWindowSession？我们进去看看

      getWindowSession(context.getMainLooper());

     ......//ViewRoot的mWindow是一个W类型，注意它不是Window类型，而是IWindow类型

       mWindow= new W(this, context);

ublic static IWindowSessiongetWindowSession(Looper mainLooper) {

synchronized (mStaticInit) {

  if(!mInitialized) {

      InputMethodManagerimm =

         InputMethodManager.getInstance(mainLooper);

      //下面这个函数先得到WindowManagerService的Binder代理，然后调用它的openSession

sWindowSession = IWindowManager.Stub.asInterface(

                   ServiceManager.getService("window"))

                 .openSession(imm.getClient(), imm.getInputContext());

                    mInitialized = true;

               } catch (RemoteException e) {

           return sWindowSession;

openSession的操作是一个使用Binder通信的跨进程调用，暂且记住这个函数，在精简流程之后再来分析。

public void setView(View view, WindowManager.LayoutParamsattrs,

                        View panelParentView){//第一个参数view是DecorView

      ......

       mView= view;//保存这个view

       synchronized (this) {

           requestLayout(); //待会先看看这个。

                    //调用IWindowSession的add函数，第一个参数是mWindow

                    res =sWindowSession.add(mWindow, mWindowAttributes,

                           getHostVisibility(), mAttachInfo.mContentInsets);

          ......

public void requestLayout() {

       checkThread();

       mLayoutRequested = true;

       scheduleTraversals();

public void scheduleTraversals() {

        if(!mTraversalScheduled) {

           mTraversalScheduled = true;

           sendEmptyMessage(DO_TRAVERSAL); //发送DO_TRAVERSAL消息

public IWindowSessionopenSession(IInputMethodClient client,

                                        IInputContextinputContext) {

       ......

return new Session(client, inputContext);

public int add(IWindow window,WindowManager.LayoutParams attrs,

               int viewVisibility, Rect outContentInsets) {

    //调用外部类对象的addWindow,也就是WMS的addWindow

    returnaddWindow(this, window, attrs, viewVisibility,

                                outContentInsets);

public int addWindow(Session session, IWindowclient,

           WindowManager.LayoutParams attrs, int viewVisibility,

           Rect outContentInsets) {

           ......

          //创建一个WindowState

          win = new WindowState(session, client, token,

                    attachedWindow, attrs,viewVisibility);

          ......

         //调用attach函数

          win.attach();

          ......

          return res;

void attach() {

      //mSession就是Session对象，调用它的windowAddedLocked函数

     mSession.windowAddedLocked();

void windowAddedLocked() {

  if(mSurfaceSession == null) {

        ......

       //创建一个SurfaceSession对象

       mSurfaceSession= new SurfaceSession();

       ......

      mNumWindow++;

void dispatchKey(in KeyEvent event);

void dispatchPointer(in MotionEvent event, longeventTime,

boolean callWhenDone);

void dispatchTrackball(in MotionEvent event,long eventTime,

boolean callWhenDone);

注意：上面的描述实际上大大简化了真实的处理流程，读者可在了解大体知识后进行更深入的研究。

public void handleMessage(Message msg) {

       switch (msg.what) {

        ......

       case DO_TRAVERSAL:

            ......

           performTraversals();//调用performTraversals函数

......

           break;

       ......

private void performTraversals() {

 finalView host = mView;//还记得这mView吗？它就是DecorView喔

  booleaninitialized = false;

  booleancontentInsetsChanged = false;

  booleanvisibleInsetsChanged;

    relayoutResult= //①关键函数relayoutWindow

relayoutWindow(params, viewVisibility,insetsPending);

......

draw(fullRedrawNeeded);// ②开始绘制

......

private intrelayoutWindow(WindowManager.LayoutParams params,

int viewVisibility, boolean insetsPending)throws RemoteException {

       //原来是调用IWindowSession的relayOut，暂且记住这个调用

       int relayoutResult = sWindowSession.relayout(

               mWindow, params,

               (int) (mView.mMeasuredWidth * appScale + 0.5f),

               (int) (mView.mMeasuredHeight * appScale + 0.5f),

               viewVisibility, insetsPending, mWinFrame,

               mPendingContentInsets, mPendingVisibleInsets,

               mPendingConfiguration, mSurface); mSurface做为参数传进去了。

   ......

private void draw(boolean fullRedrawNeeded) {

       Surface surface = mSurface;//mSurface是ViewRoot的成员变量

       ......

        Canvascanvas;

           int left = dirty.left;

           int top = dirty.top;

           int right = dirty.right;

           int bottom = dirty.bottom;

           //从mSurface中lock一块Canvas

           canvas = surface.lockCanvas(dirty);

           ......

           mView.draw(canvas);//调用DecorView的draw函数，canvas就是画布的意思啦！

           ......

           //unlock画布，屏幕上马上就会见到漂亮宝贝的长相了。

           surface.unlockCanvasAndPost(canvas);

          ......

private final Surface mSurface = new Surface();

void windowAddedLocked() {

   if(mSurfaceSession == null) {

        mSurfaceSession = new SurfaceSession();

        mNumWindow++;

private intrelayoutWindow(WindowManager.LayoutParams params,

int viewVisibility, boolean insetsPending)

throws RemoteException {

       int relayoutResult = sWindowSession.relayout(

                mWindow, params,

               (int) (mView.mMeasuredWidth * appScale + 0.5f),

               (int) (mView.mMeasuredHeight * appScale + 0.5f),

               viewVisibility, insetsPending, mWinFrame,

               mPendingContentInsets, mPendingVisibleInsets,

               mPendingConfiguration, mSurface);//mSurface传了进去

        ......

       return relayoutResult;

public int relayout(IWindow window,WindowManager.LayoutParams attrs,

               int requestedWidth, int requestedHeight, int viewFlags,

               boolean insetsPending, Rect outFrame, Rect outContentInsets,

               Rect outVisibleInsets, Configuration outConfig,

Surface outSurface) {

//注意最后这个参数的名字，叫outSurface

//调用外部类对象的relayoutWindow

   returnrelayoutWindow(this, window, attrs,

                    requestedWidth,requestedHeight, viewFlags, insetsPending,

                    outFrame, outContentInsets,outVisibleInsets, outConfig,

outSurface);

public int relayoutWindow(Session session,IWindow client,

           WindowManager.LayoutParams attrs, int requestedWidth,

           int requestedHeight, int viewVisibility, boolean insetsPending,

           Rect outFrame, Rect outContentInsets, Rect outVisibleInsets,

            Configuration outConfig, SurfaceoutSurface){

        .....

         //win就是WinState，这里将创建一个本地的Surface对象

         Surfacesurface = win.createSurfaceLocked();

          if(surface != null) {

            //先创建一个本地surface，然后在outSurface的对象上调用copyFrom

           //将本地Surface的信息拷贝到outSurface中，为什么要这么麻烦呢？

           outSurface.copyFrom(surface);

        ......

Surface createSurfaceLocked() {

     ......

     //mSurfaceSession就是在Session上创建的SurfaceSession对象

     //这里，以它为参数，构造一个新的Surface对象

        mSurface = new Surface(

                mSession.mSurfaceSession, mSession.mPid,

                 mAttrs.getTitle().toString(),

                 0, w, h, mAttrs.format, flags);

         Surface.openTransaction();//打开一个事务处理

        ......

         Surface.closeTransaction();//关闭一个事务处理。关于事务处理以后再分析

         ......

interface IWindowSession {

    ......

 intrelayout(IWindow window, in WindowManager.LayoutParams attrs,

           int requestedWidth, int requestedHeight, int viewVisibility,

           boolean insetsPending, out Rect outFrame, out Rect outContentInsets,

           out Rect outVisibleInsets, out Configuration outConfig,

           out Surface outSurface);

在命令行下可以输入：

aidl –Ie:\froyo\source\frameworks\base\core\java\ -Ie:\froyo\source\frameworks\base\Graphics\java e:\froyo\source\frameworks\base\core\java\android\view\IWindowSession.aidltest.java

新生成的Java文件叫test.java。其中，-I参数指定include目录，例如aidl文件中使用了别的Java文件中的类，所以需要指定这些Java文件所在的目录。

public int relayout(android.view.IWindow window,

                 android.view.WindowManager.LayoutParams attrs,

                  int requestedWidth, intrequestedHeight,

                 int viewVisibility, boolean insetsPending,

                 android.graphics.Rect outFrame,

                 android.graphics.Rect outContentInsets,

                 android.graphics.Rect outVisibleInsets,

                 android.content.res.Configuration outConfig,

                 android.view.Surface outSurface)//outSurface是第11个参数

                                    throwsandroid.os.RemoteException

   android.os.Parcel_data = android.os.Parcel.obtain();

   android.os.Parcel_reply = android.os.Parcel.obtain();

   int_result;

      _data.writeInterfaceToken(DESCRIPTOR);

     _data.writeStrongBinder((((window!=null))?(window.asBinder()):(null)));

     if((attrs!=null)) {

       _data.writeInt(1);

       attrs.writeToParcel(_data,0);

    else {

    _data.writeInt(0);

  _data.writeInt(requestedWidth);

  _data.writeInt(requestedHeight);

  _data.writeInt(viewVisibility);

  _data.writeInt(((insetsPending)?(1):(0)));

 //奇怪，outSurface的信息没有写到请求包_data中，就直接发送请求消息了

  mRemote.transact(Stub.TRANSACTION_relayout,_data, _reply, 0);

  _reply.readException();

  _result= _reply.readInt();

  if((0!=_reply.readInt())) {

   outFrame.readFromParcel(_reply);

  if((0!=_reply.readInt())) {

     outSurface.readFromParcel(_reply);//从Parcel中读取信息来填充outSurface

  ......

  return_result;

public boolean onTransact(int code,android.os.Parcel data,

                               android.os.Parcelreply, int flags)

                    throwsandroid.os.RemoteException

  switch(code)

    caseTRANSACTION_relayout:

      data.enforceInterface(DESCRIPTOR);

      android.view.IWindow_arg0;

      android.view.Surface_arg10;

      //刚才讲了，Surface信息并没有传过来，那么在relayOut中看到的outSurface是怎么

      //出来的呢？看下面这句可知，原来在服务端这边竟然new了一个新的Surface!!!

      _arg10= new android.view.Surface();

      int_result = this.relayout(_arg0, _arg1, _arg2, _arg3, _arg4,

      _arg5,_arg6, _arg7, _arg8, _arg9, _arg10);

      reply.writeNoException();

      reply.writeInt(_result);

      //_arg10就是调用copyFrom的那个outSurface，那怎么传到客户端呢？

      if((_arg10!=null)) {

           reply.writeInt(1);

           //调用Surface的writeToParcel，把信息写到reply包中。

           //注意最后一个参数为PARCELABLE_WRITE_RETURN_VALUE

           _arg10.writeToParcel(reply,

                 android.os.Parcelable.PARCELABLE_WRITE_RETURN_VALUE);

    ......

   returntrue;

注意，这里，将BpWindowSession作为了IWindowSessionBinder在客户端的代表。

public Surface() {

        ......

       //CompatibleCanvas从Canvas类派生

       mCanvas = new CompatibleCanvas();

public SurfaceSession() {

       init();//这是一个native函数

static void SurfaceSession_init(JNIEnv* env,jobject clazz)

     //创建一个SurfaceComposerClient对象

   sp<SurfaceComposerClient> client = new SurfaceComposerClient;

client->incStrong(clazz);

//在Java对象中保存这个client对象的指针，类型为SurfaceComposerClient

   env->SetIntField(clazz, sso.client, (int)client.get());

    publicSurface(SurfaceSession s,//传入一个SurfaceSession对象

           int pid, String name, int display, int w, int h, int format, int flags)

       throws OutOfResourcesException {

        ......

       mCanvas = new CompatibleCanvas();

      //又一个native函数，注意传递的参数：display以后再说，w,h代表绘图区域的宽高值

       init(s,pid,name,display,w,h,format,flags);

       mName = name;

static void Surface_init(

        JNIEnv*env, jobject clazz,

       jobject session,

       jint pid, jstring jname, jint dpy, jint w, jint h, jint format, jintflags)

   //从SurfaceSession对象中取出之前创建的那个SurfaceComposerClient对象

SurfaceComposerClient* client =

           (SurfaceComposerClient*)env->GetIntField(session, sso.client);

   sp<SurfaceControl> surface;//注意它的类型是SurfaceControl

if (jname == NULL) {

调用SurfaceComposerClient的createSurface函数，返回的surface是一个

SurfaceControl类型。

       surface = client->createSurface(pid, dpy, w, h, format, flags);

    } else{

        ......

   //把这个surfaceControl对象设置到Java层的Surface对象中，对这个函数就不再分析了

   setSurfaceControl(env, clazz, surface);

static void Surface_copyFrom(JNIEnv* env,jobject clazz, jobject other)

   //根据JNI函数的规则，clazz是copyFrom的调用对象，而other是copyFrom的参数。

   //目标对象此时还没有设置SurfaceControl，而源对象在前面已经创建了SurfaceControl

   constsp<SurfaceControl>& surface = getSurfaceControl(env, clazz);

   constsp<SurfaceControl>& rhs = getSurfaceControl(env, other);

if (!SurfaceControl::isSameSurface(surface, rhs)) {

        //把源SurfaceControl对象设置到目标Surface中。

       setSurfaceControl(env, clazz, rhs);

static void Surface_writeToParcel(JNIEnv* env,jobject clazz,

jobject argParcel, jint flags)

   Parcel* parcel = (Parcel*)env->GetIntField(argParcel, no.native_parcel);

//clazz就是Surface对象，从这个Surface对象中取出保存的SurfaceControl对象

const sp<SurfaceControl>&control(getSurfaceControl(env, clazz));

把SurfaceControl中的信息写到Parcel包中，然后利用Binder通信传递到对端，

对端通过readFromParcel来处理Parcel包。

   SurfaceControl::writeSurfaceToParcel(control, parcel);

if (flags & PARCELABLE_WRITE_RETURN_VALUE) {

       //还记得PARCELABLE_WRITE_RETURN_VALUE吗？flags的值就等于它

       //所以本地Surface对象的SurfaceControl值被置空了

       setSurfaceControl(env, clazz, 0);

static void Surface_readFromParcel(

       JNIEnv* env, jobject clazz, jobject argParcel)

   Parcel* parcel = (Parcel*)env->GetIntField( argParcel,no.native_parcel);

   //注意下面定义的变量类型是Surface，而不是SurfaceControl

   const sp<Surface>&control(getSurface(env, clazz));

   //根据服务端传递的Parcel包来构造一个新的surface。

   sp<Surface> rhs = new Surface(*parcel);

if (!Surface::isSameSurface(control, rhs)) {

//把这个新surface赋给ViewRoot中的mSurface对象。

      setSurface(env,clazz, rhs);

精简流程后，寥寥数语就可把过程说清楚。以后我们在研究代码时，也可以采取这种方式。

public Canvas lockCanvas(Rect dirty)

throws OutOfResourcesException,IllegalArgumentException

       return lockCanvasNative(dirty);//调用native的lockCanvasNative函数。

static jobject Surface_lockCanvas(JNIEnv* env,jobject clazz, jobject dirtyRect)

    //从Java中的Surface对象中，取出费尽千辛万苦得到的Native的Surface对象

    constsp<Surface>& surface(getSurface(env, clazz));

    ......

// dirtyRect表示需要重绘的矩形块，下面根据这个dirtyRect设置dirtyRegion

    RegiondirtyRegion;

    if(dirtyRect) {

       Rect dirty;

       dirty.left  =env->GetIntField(dirtyRect, ro.l);

       dirty.top   =env->GetIntField(dirtyRect, ro.t);

       dirty.right = env->GetIntField(dirtyRect, ro.r);

        dirty.bottom=env->GetIntField(dirtyRect, ro.b);

        if(!dirty.isEmpty()) {

           dirtyRegion.set(dirty);   

    } else{

       dirtyRegion.set(Rect(0x3FFF,0x3FFF));

//调用NativeSurface对象的lock函数，

//传入了一个参数Surface::SurfaceInfo info和一块表示脏区域的dirtyRegion

   Surface::SurfaceInfo info;

   status_t err = surface->lock(&info, &dirtyRegion);

    ......

//Java的Surface对象构造的时候会创建一个CompatibleCanvas。

//这里就取出这个CompatibleCanvas对象

   jobject canvas = env->GetObjectField(clazz, so.canvas);

   env->SetIntField(canvas, co.surfaceFormat, info.format);

    //从Canvas对象中取出SkCanvas对象

SkCanvas* nativeCanvas =(SkCanvas*)env->GetIntField(

canvas, no.native_canvas);

                         SkBitmap bitmap;

                         ssize_t bpr = info.s *bytesPerPixel(info.format);

   bitmap.setConfig(convertPixelFormat(info.format), info.w, info.h, bpr);

   ......

if (info.w > 0 && info.h > 0) {

//info.bits指向一块存储区域。

       bitmap.setPixels(info.bits);

    } else{

        bitmap.setPixels(NULL);

//给这个SkCanvas设置一个Bitmap，还记得前面说的，画图需要的四大金刚吗？

//这里将Bitmap设置到这个Canvas中，这样进UI绘画时就有画布了。

   nativeCanvas->setBitmapDevice(bitmap);

    ......

    returncanvas;

注意，本书不拟讨论Android系统上Skia和OpenGL方面的知识，有兴趣的读者可自行研究。

static void Surface_unlockCanvasAndPost(JNIEnv*env, jobject clazz,

jobject argCanvas)

    jobjectcanvas = env->GetObjectField(clazz, so.canvas);

    //取出Native的Surface对象

const sp<Surface>& surface(getSurface(env,clazz));

//下面这些内容，不拟讨论，读者若有兴趣，可结合Skia库，自行研究。

SkCanvas* nativeCanvas =(SkCanvas*)env->GetIntField(canvas,

                                                 no.native_canvas);

    intsaveCount = env->GetIntField(clazz, so.saveCount);

   nativeCanvas->restoreToCount(saveCount);

   nativeCanvas->setBitmapDevice(SkBitmap());

   env->SetIntField(clazz, so.saveCount, 0);

    //调用Surface对象的unlockAndPost函数。

   status_t err = surface->unlockAndPost();

    ......

注意，Surface系统中定义了一个名为Layer类型的类，为了区分广义概念上的Layer和代码中的Layer，这里称广义层的Layer为显示层，以免混淆。

注意，关于Surface系统的显示层属性定义，读者可参考ISurfaceComposer.h。

注意：上面所说的框架将引出另外一个概念Linux FrameBuffer（简称LFB）。LFB是Linux平台提供的一种可直接操作FB的机制，依托这个机制，应用层通过标准的系统调用，就可以操作显示设备了。从使用的角度来看，它和Linux Audio中的OSS有些类似。

struct fbinfo {//定义一个结构体

   unsigned int version;

   unsigned int bpp;

   unsigned int size;

   unsigned int width;

   unsigned int height;

   unsigned int red_offset;

   unsigned int red_length;

   unsigned int blue_offset;

   unsigned int blue_length;

   unsigned int green_offset;

   unsigned int green_length;

   unsigned int alpha_offset;

   unsigned int alpha_length;

} __attribute__((packed));

//fd是一个文件的描述符，这个函数的目的，是把当前屏幕的内容写到一个文件中

void framebuffer_service(int fd, void *cookie)

    structfb_var_screeninfo vinfo;

    intfb, offset;

    charx[256];

    structfbinfo fbinfo;

   unsigned i, bytespp;

   //Android系统上的fb设备路径在/dev/graphics目录下

    fb =open("/dev/graphics/fb0", O_RDONLY);

    if(fb< 0) goto done;

    //取出屏幕的属性

   if(ioctl(fb, FBIOGET_VSCREENINFO, &vinfo) < 0) goto done;

   fcntl(fb, F_SETFD, FD_CLOEXEC);

   bytespp = vinfo.bits_per_pixel / 8;

    //根据屏幕的属性填充fbinfo结构，这个结构要写到输出文件的头部

    fbinfo.version = DDMS_RAWIMAGE_VERSION;

   fbinfo.bpp = vinfo.bits_per_pixel;

   fbinfo.size = vinfo.xres * vinfo.yres * bytespp;

   fbinfo.width = vinfo.xres;

fbinfo.height = vinfo.yres;

下面几个变量和颜色格式有关，以RGB565为例，简单介绍一下。

RGB565表示一个像素点中R分量为5位，G分量为6位，B分量为5位，并且没有Alpha分量。

这样一个像素点的大小为16位，占两个字节，比RGB888格式的一个像素少一个字节（它一个像素是三个字节）。

x_length的值为x分量的位数，例如，RGB565中R分量就是5位。

x_offset的值代表x分量在内存中的位置。如RGB565一个像素占两个字节，那么x_offeset

表示x分量在这两个字节内存区域中的起始位置，但这个顺序是反的，也就是B分量在前，

R在最后。所以red_offset的值就是11，而blue_offset的值是0,green_offset的值是6。

这些信息在做格式转换时（例如从RGB565转到RGB888的时候）有用。

   fbinfo.red_offset = vinfo.red.offset;

   fbinfo.red_length = vinfo.red.length;

   fbinfo.green_offset = vinfo.green.offset;

   fbinfo.green_length = vinfo.green.length;

   fbinfo.blue_offset = vinfo.blue.offset;

   fbinfo.blue_length = vinfo.blue.length;

   fbinfo.alpha_offset = vinfo.transp.offset;

   fbinfo.alpha_length = vinfo.transp.length;

    offset= vinfo.xoffset * bytespp;

    offset+= vinfo.xres * vinfo.yoffset * bytespp;

    //将fb信息写到文件头部

   if(writex(fd, &fbinfo, sizeof(fbinfo))) goto done;

   lseek(fb, offset, SEEK_SET);

    for(i= 0; i < fbinfo.size; i += 256) {

     if(readx(fb, &x, 256)) goto done;//读取FBD中的数据

     if(writex(fd, &x, 256)) goto done;//将数据写到文件

   if(readx(fb, &x, fbinfo.size % 256)) goto done;

   if(writex(fd, &x, fbinfo.size % 256)) goto done;

done:

    if(fb>= 0) close(fb);

   close(fd);

注意：我们可根据这段代码，写一个简单的Native可执行程序，然后adb push到设备上运行。注意上面写到文件中的是RGB565格式的原始数据，如想在台式机上看到这幅图片，可将它转换成BMP格式。我的个人博客上提供一个RGB565转BMP的程序，读者可以下载或自己另写一个，这样或许有助于更深入理解图形/图像方面的知识。

说白了，PageFlipping其实就是使用了一个只有两个成员的帧缓冲队列，以后在分析数据传输的时候还会见到诸如dequeue和queue的操作。

static void SurfaceSession_init(JNIEnv* env,jobject clazz)

  //new 一个SurfaceComposerClient对象

sp<SurfaceComposerClient> client = newSurfaceComposerClient;

//sp的使用也有让人烦恼的地方，有时需要显式地增加强弱引用计数，要是忘记，可就麻烦了

client->incStrong(clazz);

 env->SetIntField(clazz, sso.client,(int)client.get());

SurfaceComposerClient::SurfaceComposerClient()

  //getComposerService()将返回SF的Binder代理端的BpSurfaceFlinger对象

sp<ISurfaceComposer> sm(getComposerService());

//先调用SF的createConnection，再调用_init

  _init(sm, sm->createConnection());

    if(mClient != 0) {

       Mutex::Autolock _l(gLock);

       //gActiveConnections是全局变量，把刚才创建的client保存到这个map中去

       gActiveConnections.add(mClient->asBinder(), this);

sp<ISurfaceFlingerClient>SurfaceFlinger::createConnection()

   Mutex::Autolock _l(mStateLock);

   uint32_t token = mTokens.acquire();

   //先创建一个Client。

   sp<Client> client = new Client(token, this);

    //把这个Client对象保存到mClientsMap中，token是它的标识。

   status_t err = mClientsMap.add(token, client);

创建一个用于Binder通信的BClient，BClient派生于ISurfaceFlingerClient，

它的作用是接受客户端的请求，然后把处理提交给SF，注意，并不是提交给Client。

Client会创建一块共享内存，该内存由getControlBlockMemory函数返回

   sp<BClient> bclient =

        new BClient(this, token,client->getControlBlockMemory());

    returnbclient;

Client::Client(ClientID clientID, constsp<SurfaceFlinger>& flinger)

    :ctrlblk(0), cid(clientID), mPid(0), mBitmap(0), mFlinger(flinger)

const int pgsize = getpagesize();

//下面这个操作会使cblksize为页的大小，目前是4096字节。

    constint cblksize = ((sizeof(SharedClient)+(pgsize-1))&~(pgsize-1));

    //MemoryHeapBase是我们的老朋友了，不熟悉的读者可以回顾Audio系统中所介绍的内容

   mCblkHeap = new MemoryHeapBase(cblksize, 0,

                "SurfaceFlinger Clientcontrol-block");

   ctrlblk = static_cast<SharedClient *>(mCblkHeap->getBase());

    if(ctrlblk) {

       new(ctrlblk) SharedClient; //再一次觉得眼熟吧？使用了placement new

class SharedClient

public:

   SharedClient();

   ~SharedClient();

   status_t validate(size_t token) const;

   uint32_t getIdentity(size_t token) const;//取出标识本Client的token

private:

    Mutexlock;

Condition cv; //支持跨进程的同步对象

//NUM_LAYERS_MAX为31，SharedBufferStack是什么？

   SharedBufferStack surfaces[ NUM_LAYERS_MAX ];

//SharedClient的构造函数，没什么新意，不如Audio的CB对象复杂

SharedClient::SharedClient()

    :lock(Mutex::SHARED), cv(Condition::SHARED)

class  SharedBufferStack{

     ......

    //Buffer是按块使用的，每个Buffer都有自己的编号，其实就是数组中的索引号。

   volatile int32_t head;     //FrontBuffer的编号

   volatile int32_t available; //空闲Buffer的个数

   volatile int32_t queued;  //脏Buffer的个数，脏Buffer表示有新数据的Buffer

   volatile int32_t inUse; //SF当前正在使用的Buffer的编号   

    volatilestatus_t status; //状态码

     ......

注意，这里的显示层指的是Normal类型的显示层。

SurfaceComposerClient::SurfaceComposerClient()

   ......

   _init(sm, sm->createConnection());

   ......

void SurfaceComposerClient::_init(

       const sp<ISurfaceComposer>& sm, constsp<ISurfaceFlingerClient>& conn)

   mPrebuiltLayerState = 0;

   mTransactionOpen = 0;

   mStatus = NO_ERROR;

   mControl = 0;

   mClient = conn;//mClient就是BClient的客户端

    mControlMemory =mClient->getControlBlock();

mSignalServer = sm;// mSignalServer就是BpSurfaceFlinger

//mControl就是那个创建于共享内存之中的SharedClient

    mControl = static_cast<SharedClient*>(mControlMemory->getBase());

static void Surface_init(JNIEnv* env, jobjectclazz, jobject session,

       jint pid, jstring jname, jint dpy, jint w, jint h, jint format, jintflags)

    SurfaceComposerClient* client =

           (SurfaceComposerClient*)env->GetIntField(session, sso.client);

    //注意这个变量，类型是SurfaceControl，名字却叫surface，稍不留神就出错了。

    sp<SurfaceControl>surface;

if (jname == NULL) {

    //调用Client的createSurface函数，得到一个SurfaceControl对象。

    surface= client->createSurface(pid, dpy, w, h, format, flags);

......

   //将这个SurfaceControl对象设置到Java层的对象中保存。

   setSurfaceControl(env, clazz, surface);

此时，读者或许会被代码中随意起的变量名搞糊涂，因为我的处理方法碰到了容易混淆的地方，尽量以对象类型来表示这个对象。

sp<SurfaceControl>SurfaceComposerClient::createSurface(

       int pid,

       DisplayID display,//DisplayID是什么意思？

       uint32_t w,

       uint32_t h,

       PixelFormat format,

       uint32_t flags)

   String8 name;

    constsize_t SIZE = 128;

    charbuffer[SIZE];

   snprintf(buffer, SIZE, "<pid_%d>", getpid());

   name.append(buffer);

   //调用另外一个createSurface，多一个name参数

    returnSurfaceComposerClient::createSurface(pid, name, display,

           w, h, format, flags);

typedef int32_t    DisplayID;

sp<SurfaceControl>SurfaceComposerClient::createSurface(

       int pid,const String8& name,DisplayID display,uint32_t w,

       uint32_t h,PixelFormat format,uint32_t flags)

   sp<SurfaceControl> result;

    if(mStatus == NO_ERROR) {

       ISurfaceFlingerClient::surface_data_t data;

        //调用BpSurfaceFlingerClient的createSurface函数

       sp<ISurface> surface = mClient->createSurface(&data, pid,name,

                                 display, w, h,format, flags);

        if(surface != 0) {

           if (uint32_t(data.token) < NUM_LAYERS_MAX) {

               //以返回的ISurface对象创建一个SurfaceControl对象

               result = new SurfaceControl(this, surface, data, w, h,

format, flags);

    returnresult;//返回的是SurfaceControl对象

在Surface系统定义了很多类型，咱们也中途休息一下，不妨来看看和字符串“Surface”有关的有多少个类，权当其为小小的娱乐：

Native层有Surface、ISurface、SurfaceControl、SurfaceComposerClient。

Java层有Surface、SurfaceSession。

上面列出的还只是一部分，后面还有呢！*&@&*%￥*

sp<ISurface> BClient::createSurface(

       ISurfaceFlingerClient::surface_data_t* params, int pid,

       const String8& name,

       DisplayID display, uint32_t w, uint32_t h, PixelFormat format,

       uint32_t flags)

  //果然是交给SF处理，以后我们将跳过BClient这个代理。 

return mFlinger->createSurface(mId, pid,name, params, display, w, h,

           format, flags);

sp<ISurface>SurfaceFlinger::createSurface(ClientID clientId, int pid,

       const String8& name, ISurfaceFlingerClient::surface_data_t* params,

       DisplayID d, uint32_t w, uint32_t h, PixelFormat format,

       uint32_t flags)

sp<LayerBaseClient> layer;//LayerBaseClient是Layer家族的基类

//这里又冒出一个LayerBaseClient的内部类，它也叫Surface，是不是有点头晕了？

   sp<LayerBaseClient::Surface> surfaceHandle;

Mutex::Autolock _l(mStateLock);

//根据clientId找到createConnection时加入的那个Client对象

   sp<Client> client = mClientsMap.valueFor(clientId);

    ......

   //注意这个id，它的值表示Client创建的是第几个显示层，根据图8-14可以看出，这个id

//同时也表示将使用SharedBufferStatck数组的第id个元素。

int32_t id = client->generateId(pid);

//一个Client不能创建多于NUM_LAYERS_MAX个的Layer。

    if(uint32_t(id) >= NUM_LAYERS_MAX) {

       return surfaceHandle;

   //根据flags参数来创建不同类型的显示层，我们在8.4.1节介绍过相关知识

    switch(flags & eFXSurfaceMask) {

       case eFXSurfaceNormal:

           if (UNLIKELY(flags & ePushBuffers)) {

             //创建PushBuffer类型的显示层，我们将在拓展思考部分分析它

            layer = createPushBuffersSurfaceLocked(client, d, id,

                        w, h, flags);

           } else {

               //①创建Normal类型的显示层，我们分析待会这个

               layer = createNormalSurfaceLocked(client, d, id,

                        w, h, flags, format);

           break;

       case eFXSurfaceBlur:

            //创建Blur类型的显示层

           layer = createBlurSurfaceLocked(client, d, id, w, h, flags);

           break;

        case eFXSurfaceDim:

            //创建Dim类型的显示层

           layer = createDimSurfaceLocked(client, d, id, w, h, flags);

           break;

    if(layer != 0) {

       layer->setName(name);

       setTransactionFlags(eTransactionNeeded);

//从显示层对象中取出一个ISurface对象赋值给SurfaceHandle

       surfaceHandle = layer->getSurface();

        if(surfaceHandle != 0) {

           params->token = surfaceHandle->getToken();

           params->identity = surfaceHandle->getIdentity();

           params->width = w;

           params->height = h;

           params->format = format;

    returnsurfaceHandle;//ISurface的Bn端就是这个对象。

sp<LayerBaseClient>SurfaceFlinger::createNormalSurfaceLocked(

       const sp<Client>& client, DisplayID display,

       int32_t id, uint32_t w, uint32_t h, uint32_t flags,

       PixelFormat& format)

    switch(format) { //一些图像方面的参数设置，可以不去管它。

    casePIXEL_FORMAT_TRANSPARENT:

    casePIXEL_FORMAT_TRANSLUCENT:

       format = PIXEL_FORMAT_RGBA_8888;

       break;

    casePIXEL_FORMAT_OPAQUE:

       format = PIXEL_FORMAT_RGB_565;

       break;

    //①创建一个Layer类型的对象

sp<Layer> layer = new Layer(this, display,client, id);

//②设置Buffer

   status_t err = layer->setBuffers(w, h, format, flags);

if (LIKELY(err == NO_ERROR)) {

         //初始化这个新layer的一些状态

       layer->initStates(w, h, flags);

       //③ 还记得在图8-10中提到的Z轴吗？下面这个函数把这个layer加入到Z轴大军中。

       addLayer_l(layer);

......

    returnlayer;

result = new SurfaceControl(this, surface, data,w, h,format, flags);

SurfaceControl::SurfaceControl(

       const sp<SurfaceComposerClient>& client,

       const sp<ISurface>& surface,

       const ISurfaceFlingerClient::surface_data_t& data,

       uint32_t w, uint32_t h, PixelFormat format, uint32_t flags)

    //mClient为SurfaceComposerClient，而mSurface指向跨进程createSurface调用

//返回的ISurface对象。

    :mClient(client), mSurface(surface),

     mToken(data.token), mIdentity(data.identity),

     mWidth(data.width), mHeight(data.height), mFormat(data.format),

     mFlags(flags)

Layer::Layer(SurfaceFlinger* flinger, DisplayIDdisplay,

       const sp<Client>& c, int32_t i)//这个i表示SharedBufferStack数组的索引

    :   LayerBaseClient(flinger, display, c, i),//先调用基类构造函数

       mSecure(false),

       mNoEGLImageForSwBuffers(false),

       mNeedsBlending(true),

       mNeedsDithering(false)

     //getFrontBuffer实际取出的是FrontBuffer的位置

   mFrontBufferIndex = lcblk->getFrontBuffer();

LayerBaseClient::LayerBaseClient(SurfaceFlinger*flinger, DisplayID display,

       const sp<Client>& client, int32_t i)

    :LayerBase(flinger, display), lcblk(NULL), client(client), mIndex(i),

      mIdentity(uint32_t(android_atomic_inc(&sIdentity)))

    创建一个SharedBufferServer对象，注意它使用了SharedClient对象，

    并且传入了表示SharedBufferStack数组索引的i和一个常量NUM_BUFFERS

lcblk = new SharedBufferServer(

           client->ctrlblk, i, NUM_BUFFERS,//该值为常量2，在Layer.h中定义

           mIdentity);

注意，在拓展思考部分，会有单独章节来分析生产/消费过程中的读写控制。

void LayerBaseClient::onFirstRef()

   sp<Client> client(this->client.promote());

if (client != 0) {

//把自己加入client对象的mLayers数组中,这部分内容比较简单，读者可以自行研究

       client->bindLayer(this, mIndex);

status_t Layer::setBuffers( uint32_t w, uint32_th,

                            PixelFormat format,uint32_t flags)

   PixelFormatInfo info;

   status_t err = getPixelFormatInfo(format, &info);

    if(err) return err;

//DisplayHardware是代表显示设备的HAL对象，0代表第一块屏幕的显示设备。

//这里将从HAL中取出一些和显示相关的信息。

    constDisplayHardware& hw(graphicPlane(0).displayHardware());

   uint32_t const maxSurfaceDims = min(

           hw.getMaxTextureSize(), hw.getMaxViewportDims());

   PixelFormatInfo displayInfo;

    getPixelFormatInfo(hw.getFormat(),&displayInfo);

    constuint32_t hwFlags = hw.getFlags();

    ......

创建Buffer，这里将创建两个GraphicBuffer。这两个GraphicBuffer就是我们前面

所说的FrontBuffer和BackBuffer。

for (size_t i=0 ; i<NUM_BUFFERS ; i++) {

//注意，这里调用的是GraphicBuffer的无参构造函数,mBuffers是一个二元数组。

       mBuffers[i] = new GraphicBuffer();

//又冒出来一个SurfaceLayer类型，#￥%……&*！@

   mSurface = new SurfaceLayer(mFlinger, clientIndex(), this);

    returnNO_ERROR;

GraphicBuffer是Android提供的显示内存管理类，关于它的故事，将在8.4.7节中介绍。我们暂把它当做普通的Buffer即可。

status_t SurfaceFlinger::addLayer_l(constsp<LayerBase>& layer)

mCurrentState是SurfaceFlinger定义的一个结构，它有一个成员变量叫

layersSortedByZ，其实就是一个排序数组。下面这个add函数将把这个新的layer按照

它在Z轴的位置加入到排序数组中。mCurrentState保存了所有的显示层。

    ssize_t i = mCurrentState.layersSortedByZ.add(

                             layer,&LayerBase::compareCurrentStateZ);

sp<LayerBaseClient> lbc =

LayerBase::dynamicCast< LayerBaseClient*>(layer.get());

    if(lbc != 0) {

       mLayerMap.add(lbc->serverIndex(), lbc);

    returnNO_ERROR;

强烈建议Google把Surface相关代码好好整理一下，至少让类型名取得更直观些，现在这样确实有点让人头晕。好，来小小娱乐一下。看之前介绍的和“Surface”有关的名字：

Native层有Surface、ISurface、SurfaceControl、SurfaceComposerClient。

Java层有Surface、SurfaceSession。

在介绍完Layer家族后，与它相关的名字又多了几个，它们是

LayerBaseClient::Surface、Layer::SurfaceLayer、LayerBuffer::SurfaceLayerBuffer。

注意，mOwner变量由SurfaceLayer的基类Surface（LayBaseClient的内部类）定义。

后文将Activity所在的进程简称为Activity端。

status_t SurfaceControl::writeSurfaceToParcel(

       const sp<SurfaceControl>& control, Parcel* parcel)

   uint32_t flags = 0;

   uint32_t format = 0;

   SurfaceID token = -1;

   uint32_t identity = 0;

   uint32_t width = 0;

   uint32_t height = 0;

   sp<SurfaceComposerClient> client;

   sp<ISurface> sur;

    if(SurfaceControl::isValid(control)) {

       token    = control->mToken;

        identity= control->mIdentity;

       client   = control->mClient;

       sur      = control->mSurface;

       width    = control->mWidth;

       height   = control->mHeight;

       format   = control->mFormat;

       flags    = control->mFlags;

//SurfaceComposerClient的信息需要传递到Activity端，这样客户端那边会构造一个

//SurfaceComposerClient对象

parcel->writeStrongBinder(client!=0  ? client->connection() : NULL);

//把ISurface对象信息也写到Parcel中，这样Activity端那边也会构造一个ISurface对象

    parcel->writeStrongBinder(sur!=0?sur->asBinder(): NULL);

   parcel->writeInt32(token);

   parcel->writeInt32(identity);

   parcel->writeInt32(width);

   parcel->writeInt32(height);

   parcel->writeInt32(format);

   parcel->writeInt32(flags);

    returnNO_ERROR;

static void Surface_readFromParcel(

       JNIEnv* env, jobject clazz, jobject argParcel)

   Parcel* parcel = (Parcel*)env->GetIntField( argParcel, no.native_parcel);

const sp<Surface>& control(getSurface(env,clazz));

//根据服务端的parcel信息来构造客户端的Surface

   sp<Surface> rhs = new Surface(*parcel);

    if(!Surface::isSameSurface(control, rhs)) {

         setSurface(env, clazz, rhs);

Surface::Surface(const Parcel& parcel)

:mBufferMapper(GraphicBufferMapper::get()),

mSharedBufferClient(NULL)

Surface定义了一个mBuffers变量，它是一个sp<GraphicBuffer>的二元数组，也就是说Surface也存在二个GraphicBuffer，而之前在创建Layer的时候也有两个GraphicBuffer，难道一共有四个GraphicBuffer？这个问题，后面再解答。

sp<IBinder> clientBinder =parcel.readStrongBinder();

//得到ISurface的Bp端BpSurface。

   mSurface    =interface_cast<ISurface>(parcel.readStrongBinder());

   mToken      = parcel.readInt32();

   mIdentity   = parcel.readInt32();

   mWidth      = parcel.readInt32();

   mHeight     = parcel.readInt32();

   mFormat     = parcel.readInt32();

   mFlags      = parcel.readInt32();

if (clientBinder != NULL) {

根据ISurfaceFlingerClient对象构造一个SurfaceComposerClient对象，注意我们

现在位于Activity端，这里还没有创建SurfaceComposerClient对象，所以需要创建一个

       mClient = SurfaceComposerClient::clientForConnection(clientBinder);

       //SharedBuffer家族的最后一员ShardBufferClient终于出现了。

       mSharedBufferClient = new SharedBufferClient(

                             mClient->mControl, mToken, 2,mIdentity);

   init();//做一些初始化工作。

SharedBufferBase::SharedBufferBase(SharedClient*sharedClient,

       int surface, int num, int32_t identity)

: mSharedClient(sharedClient),

  mSharedStack(sharedClient->surfaces+ surface),

 mNumBuffers(num), //根据前面PageFlipping的知识可知，num值为2

mIdentity(identity)

上面的赋值语句中最重要的是第二句：

   mSharedStack(sharedClient->surfaces +surface)

   这条语句使得这个SharedBufferXXX对象，和SharedClient中SharedBufferStack数组

的第surface个元素建立了关系

status_t Surface::lock(SurfaceInfo* other,Region* dirtyIn, bool blocking)

    //传入的参数中，other用来接收一些返回信息，dirtyIn表示需要重绘的区域  

......

if (mApiLock.tryLock() != NO_ERROR) {//多线程的情况下要锁住

     ......

     returnWOULD_BLOCK;

    //设置usage标志，这个标志在GraphicBuffer分配缓冲时有指导作用

   setUsage(GRALLOC_USAGE_SW_READ_OFTEN | GRALLOC_USAGE_SW_WRITE_OFTEN);

    //定义一个GraphicBuffer，名字就叫backBuffer。

    sp<GraphicBuffer>backBuffer;

   //①还记得我们说的2个元素的缓冲队列吗？下面的dequeueBuffer将取出一个空闲缓冲

    status_terr = dequeueBuffer(&backBuffer);

   if (err== NO_ERROR) {

        //② 锁住这块buffer

       err = lockBuffer(backBuffer.get());

        if(err == NO_ERROR) {

           const Rect bounds(backBuffer->width, backBuffer->height);

           Region scratch(bounds);

           Region& newDirtyRegion(dirtyIn ? *dirtyIn : scratch);

          ......

         //mPostedBuffer是上一次绘画时使用的Buffer，也就是现在的frontBuffer

           const sp<GraphicBuffer>& frontBuffer(mPostedBuffer);

           if (frontBuffer !=0 &&

               backBuffer->width  ==frontBuffer->width &&

               backBuffer->height == frontBuffer->height &&

               !(mFlags & ISurfaceComposer::eDestroyBackbuffer))

               const Region copyback(mOldDirtyRegion.subtract(newDirtyRegion));

               if (!copyback.isEmpty() && frontBuffer!=0) {

                    /③把frontBuffer中的数据拷贝到BackBuffer中，这是为什么？

                    copyBlt(backBuffer,frontBuffer, copyback);

            mDirtyRegion = newDirtyRegion;

           mOldDirtyRegion = newDirtyRegion;

           void* vaddr;

           //调用GraphicBuffer的lock得到一块内存，内存地址被赋值给了vaddr,

          //后续的作画将在这块内存上展开

           status_t res = backBuffer->lock(

                    GRALLOC_USAGE_SW_READ_OFTEN |GRALLOC_USAGE_SW_WRITE_OFTEN,

                    newDirtyRegion.bounds(),&vaddr);

           mLockedBuffer = backBuffer;

           //other用来接收一些信息。

           other->w      =backBuffer->width;  //宽度信息

           other->h      =backBuffer->height;

           other->s      =backBuffer->stride;

           other->usage  =backBuffer->usage;

           other->format = backBuffer->format;

           other->bits   = vaddr; //最重要的是这个内存地址

   mApiLock.unlock();

    returnerr;

status_tSurface::dequeueBuffer(sp<GraphicBuffer>* buffer) {

   android_native_buffer_t* out;

   status_t err = dequeueBuffer(&out);//调用另外一个dequeueBuffer

    if(err == NO_ERROR) {

       *buffer = GraphicBuffer::getSelf(out);

    returnerr;

intSurface::dequeueBuffer(android_native_buffer_t** buffer)

sp<SurfaceComposerClient> client(getClient());

//①调用SharedBufferClient的dequeue函数，它返回当前空闲的缓冲号

  ssize_tbufIdx = mSharedBufferClient->dequeue();

const uint32_t usage(getUsage());

mBuffers就是我们前面在Surface创建中介绍的那个二元sp<GraphicBuffer>数组。

这里定义的backBuffer是一个引用类型，也就是说如果修改backBuffer的信息，

就相当于修改了mBuffers[bufIdx]

const sp<GraphicBuffer>&backBuffer(mBuffers[bufIdx]);

//mBuffers定义的GraphicBuffer使用的也是无参构造函数，所以此时还没有真实的存储被创建

   if(backBuffer == 0 || //第一次进来满足backBuffer为空这个条件

       ((uint32_t(backBuffer->usage) & usage) != usage) ||

       mSharedBufferClient->needNewBuffer(bufIdx))

   //调用getBufferLocked，需要进去看看。

       err = getBufferLocked(bufIdx, usage);

        if(err == NO_ERROR) {

           mWidth  =uint32_t(backBuffer->width);

           mHeight = uint32_t(backBuffer->height);

......

tatus_t Surface::getBufferLocked(int index, intusage)

   sp<ISurface> s(mSurface);

   status_t err = NO_MEMORY;

//注意这个currentBuffer也被定义为引用类型

sp<GraphicBuffer>&currentBuffer(mBuffers[index]);

//终于用上了ISurface对象,调用它的requestBuffer得到指定索引index的Buffer

    sp<GraphicBuffer> buffer =s->requestBuffer(index, usage);

    if (buffer != 0) {

       err = mSharedBufferClient->getStatus();

        if(!err && buffer->handle != NULL) {

//getBufferMapper返回GraphicBufferMapper对象

//调用它的registerBuffer干什么？这个问题我们在8.4.7节回答

           err = getBufferMapper().registerBuffer(buffer->handle);

           if (err == NO_ERROR) {

         //把requestBuffer得到的值赋给currentBuffer，由于currentBuffer是引用类型，

         //实际上相当于mBuffers[index]=buffer

                currentBuffer = buffer;

               //设置currentBuffer的编号

               currentBuffer->setIndex(index);

               mNeedFullUpdate = true;

        }else {

           err = err<0 ? err : NO_MEMORY;

        return err;

sp<GraphicBuffer> Layer::requestBuffer(intindex, int usage)

   sp<GraphicBuffer> buffer;

   sp<Client> ourClient(client.promote());

  //lcblk就是那个SharedBufferServer对象，下面这个调用确保index号GraphicBuffer

  //没有被SF当做FrontBuffer使用。

   status_t err = lcblk->assertReallocate(index);

    ......

    if(err != NO_ERROR) {

        return buffer;

   uint32_t w, h;

       Mutex::Autolock _l(mLock);

        w= mWidth;

        h= mHeight;

   mBuffers是SF端创建的一个二元数组，这里取出第index个元素，之前说过，

   mBuffers使用的也是GraphicBuffer的无参构造函数，所以此时也没有真实存储被创建。

       buffer = mBuffers[index];

       mBuffers[index].clear();

    constuint32_t effectiveUsage = getEffectiveUsage(usage);

   if(buffer!=0 && buffer->getStrongCount() == 1) {

        //①分配物理存储，后面会分析这个。

       err = buffer->reallocate(w, h, mFormat, effectiveUsage);

    } else{

       buffer.clear();

       //使用GraphicBuffer的有参构造，这也使得物理存储被分配

       buffer = new GraphicBuffer(w, h, mFormat, effectiveUsage);

       err = buffer->initCheck();

    ......

    if(err == NO_ERROR && buffer->handle != 0) {

       Mutex::Autolock _l(mLock);

        if(mWidth && mHeight) {

           mBuffers[index] = buffer;

           mTextures[index].dirty = true;

        }else {

            buffer.clear();

    returnbuffer;//返回

int Surface::lockBuffer(android_native_buffer_t*buffer)

   sp<SurfaceComposerClient> client(getClient());

   status_t err = validate();

   int32_t bufIdx = GraphicBuffer::getSelf(buffer)->getIndex();

    err =mSharedBufferClient->lock(bufIdx); //调用SharedBufferClient的lock

    return err;

status_t SharedBufferClient::lock(int buf)

   LockCondition condition(this, buf);//这个buf是BackBuffer的索引号

   status_t err = waitForCondition(condition);

    returnerr;

template <typename T> //这是一个模板函数

status_t SharedBufferBase::waitForCondition(Tcondition)

    constSharedBufferStack& stack( *mSharedStack );

   SharedClient& client( *mSharedClient );

    constnsecs_t TIMEOUT = s2ns(1);

   Mutex::Autolock _l(client.lock);

    while((condition()==false) && //注意这个condition()的用法

           (stack.identity == mIdentity) &&

           (stack.status == NO_ERROR))

       status_t err = client.cv.waitRelative(client.lock, TIMEOUT);

        if(CC_UNLIKELY(err != NO_ERROR)) {

           if (err == TIMED_OUT) {

               if (condition()) {//注意这个：condition()，condition是一个对象

                   break;

               } else {

           } else {

              return err;

    return(stack.identity != mIdentity) ? status_t(BAD_INDEX) : stack.status;

这就是Funcition Object（函数对象）的概念。函数对象的本质是一个对象，不过是重载了操作符()，这和重载操作符+、-等没什么区别。可以把它当作是一个函数来看待。

为什么需要函数对象呢？因为对象可以保存信息，所以调用这个对象的()函数就可以利用这个对象的信息了。

boolSharedBufferClient::LockCondition::operator()() {

   //stack、buf等都是这个对象的内部成员，这个对象的目的就是根据读写位置判断这个buffer是

//否空闲。

    return(buf != stack.head ||

           (stack.queued > 0 && stack.inUse != buf));

status_t Surface::lock(SurfaceInfo* other,Region* dirtyIn, bool blocking)

          ......

           const sp<GraphicBuffer>& frontBuffer(mPostedBuffer);

           if (frontBuffer !=0 &&

               backBuffer->width  ==frontBuffer->width &&

               backBuffer->height == frontBuffer->height &&

               !(mFlags & ISurfaceComposer::eDestroyBackbuffer))

               const Region copyback(mOldDirtyRegion.subtract(newDirtyRegion));

               if (!copyback.isEmpty() && frontBuffer!=0) {

                    //③把frontBuffer中的数据拷贝到BackBuffer中，这是为什么？

                    copyBlt(backBuffer,frontBuffer, copyback);

    ......

status_t Surface::unlockAndPost()

    //调用GraphicBuffer的unlock函数

status_t err = mLockedBuffer->unlock();

//get返回这个GraphicBuffer的编号，queueBuffer将含有新数据的缓冲加入队中。

    err =queueBuffer(mLockedBuffer.get());

   mPostedBuffer = mLockedBuffer; //保存这个BackBuffer为mPostedBuffer

   mLockedBuffer = 0;

    returnerr;

intSurface::queueBuffer(android_native_buffer_t* buffer)

   sp<SurfaceComposerClient> client(getClient());

int32_t bufIdx =GraphicBuffer::getSelf(buffer)->getIndex();

//设置脏Region

mSharedBufferClient->setDirtyRegion(bufIdx,mDirtyRegion);

//更新写位置。

    err =mSharedBufferClient->queue(bufIdx);

     if (err== NO_ERROR) {

     //client是BpSurfaceFlinger，调用它的signalServer，这样SF就知道新数据准备好了

       client->signalServer();

    returnerr;

status_t SharedBufferClient::queue(int buf)

    //QueueUpdate也是一个函数对象

QueueUpdate update(this);

//调用updateCondition函数。

   status_t err = updateCondition( update );

   SharedBufferStack& stack( *mSharedStack );

    constnsecs_t now = systemTime(SYSTEM_TIME_THREAD);

   stack.stats.totalTime = ns2us(now - mDequeueTime[buf]);

    returnerr;

template <typename T>

status_t SharedBufferBase::updateCondition(Tupdate) {

   SharedClient& client( *mSharedClient );

   Mutex::Autolock _l(client.lock);

   ssize_t result = update();//调用update对象的()函数

   client.cv.broadcast(); //触发同步对象

    returnresult;

class GraphicBuffer

    :public EGLNativeBase<android_native_buffer_t,

               GraphicBuffer,LightRefBase<GraphicBuffer>>,

public Flattenable

template <typename NATIVE_TYPE, typenameTYPE, typename REF>

class EGLNativeBase : public NATIVE_TYPE, publicREF

typedef struct android_native_buffer_t

#ifdef __cplusplus

   android_native_buffer_t() {

       common.magic = ANDROID_NATIVE_BUFFER_MAGIC;

       common.version = sizeof(android_native_buffer_t);

       memset(common.reserved, 0, sizeof(common.reserved));

#endif

   //这个android_native_base_t是struct的第一个成员，根据C/C++编译的特性，这个成员

  //在它的派生类对象所占有的内存中也是排第一个。

    structandroid_native_base_t common;

    intwidth;

    intheight;

    intstride;

    intformat;

    intusage;

void* reserved[2];

//这是一个关键成员，保存一些和显示内存分配/管理相关的内容

   buffer_handle_t handle;

    void*reserved_proc[8];

} android_native_buffer_t;

typedef const native_handle* buffer_handle_t;

typedef struct

    intversion;        /* version值为sizeof(native_handle_t) */

    intnumFds;       

    intnumInts;       

    intdata[0];        /* data是数据存储空间的首地址 */

} native_handle_t;

typedef native_handle_t native_handle;

GraphicBuffer::GraphicBuffer()

    :BASE(), mOwner(ownData), mBufferMapper(GraphicBufferMapper::get()),

     mInitCheck(NO_ERROR), mVStride(0), mIndex(-1)

其中mBufferMapper为GraphicBufferMapper类型，它的创建采用的是单例模式，也就是每个

进程只有一个GraphicBufferMapper对象，读者可以去看看get的实现。

   width  =

    height=

    stride=

    format=

   usage  = 0;

    handle= NULL; //handle为空

status_t GraphicBuffer::reallocate(uint32_t w,uint32_t h, PixelFormat f,

       uint32_t reqUsage)

    if(mOwner != ownData)

       return INVALID_OPERATION;

    if(handle) {//handle值在无参构造函数中初始化为空，所以不满足if的条件

       GraphicBufferAllocator& allocator(GraphicBufferAllocator::get());

       allocator.free(handle);

       handle = 0;

    returninitSize(w, h, f, reqUsage);//调用initSize函数

status_t GraphicBuffer::initSize(uint32_t w,uint32_t h, PixelFormat format,

       uint32_t reqUsage)

    if(format == PIXEL_FORMAT_RGBX_8888)

       format = PIXEL_FORMAT_RGBA_8888;

GraphicBufferAllocator才是真正的存储分配的管理类，它的创建也是采用的单例模式，

也就是每个进程只有一个GraphicBufferAllocator对象

GraphicBufferAllocator& allocator =GraphicBufferAllocator::get();

//调用GraphicBufferAllocator的alloc来分配存储，注意handle作为指针

//被传了进去，看来handle的值会被修改

   status_t err = allocator.alloc(w, h, format, reqUsage, &handle,&stride);

    if(err == NO_ERROR) {

       this->width  = w;

       this->height = h;

       this->format = format;

       this->usage  = reqUsage;

       mVStride = 0;

    returnerr;

GraphicBufferAllocator::GraphicBufferAllocator()

    :mAllocDev(0)

hw_module_t const* module;

//调用hw_get_module，得到hw_module_t

    interr = hw_get_module(GRALLOC_HARDWARE_MODULE_ID, &module);

if (err == 0) {

    //调用gralloc_open函数，注意我们把module参数传了进去。

       gralloc_open(module, &mAllocDev);

读者可通过执行adb getprop ro.board.platform命令，得到具体手机上硬件平台的名字。图8-22总结了GraphicBufferAllocator分配内存的途径。这部分代码，读者可参考hardware/libhardware/hardware.c和hardware/msm7k/libgralloc-qsd8k/gralloc.cpp，后文将不再深入探讨和硬件平台有关的知识。

注意，这里是以G7的libgralloc.qsk-8k.so为示例的。其中pmem设备用来创建一块连续的内存，因为有些硬件设备（例如Camera）工作时需要使用一块连续的内存，对于这种情况，一般就会使用pmem设备来分配内存。

status_t GraphicBufferAllocator::alloc(uint32_tw, uint32_t h, PixelFormat format,int usage, buffer_handle_t* handle, int32_t*stride)

   //根据前面的定义可知buffer_handle_t为native_handle_t*类型

   status_t err;

if (usage & GRALLOC_USAGE_HW_MASK) {

    err =mAllocDev->alloc(mAllocDev, w, h, format, usage, handle, stride);

} else {

       //SW分配，可以做到和HW无关了。

       err = sw_gralloc_handle_t::alloc(w, h, format, usage, handle, stride);

......

    returnerr;

status_t sw_gralloc_handle_t::alloc(uint32_t w,uint32_t h, int format,

        int usage, buffer_handle_t* pHandle, int32_t*pStride)

    intalign = 4;

    intbpp = 0;

    ......//格式转换

    size_tbpr = (w*bpp + (align-1)) & ~(align-1);

    size_tsize = bpr * h;

    size_tstride = bpr / bpp;

    size =(size + (PAGE_SIZE-1)) & ~(PAGE_SIZE-1);

    //直接使用了ashmem创建共享内存

    int fd= ashmem_create_region("sw-gralloc-buffer", size);

   ......

    //进行内存映射，得到共享内存起始地址

    void*base = mmap(0, size, prot, MAP_SHARED, fd, 0);

sw_gralloc_handle_t* hnd = new sw_gralloc_handle_t();

   hnd->fd = fd;//保存文件描述符

   hnd->size = size;//保存共享内存的大小

   hnd->base = intptr_t(base);//intptr_t将void*类型转换成int*类型

   hnd->prot = prot;//保存属性

   *pStride = stride;

   *pHandle = hnd; //pHandle就是传入的那个handle变量的指针，这里对它进行赋值

    returnNO_ERROR;

//requestBuffer的响应端

status_t BnSurface::onTransact(

   uint32_t code, const Parcel& data, Parcel* reply, uint32_t flags)

   switch(code) {

       case REQUEST_BUFFER: {

           CHECK_INTERFACE(ISurface, data, reply);

           int bufferIdx = data.readInt32();

           int usage = data.readInt32();

           sp<GraphicBuffer> buffer(requestBuffer(bufferIdx, usage));

           ......

requestBuffer的返回值被写到Parcel包中，由于GraphicBuffer从

Flattenable类派生，这将导致它的flatten函数被调用

           return reply->write(*buffer);

      .......

//再来看请求端的处理，在BpSurface中

virtual sp<GraphicBuffer> requestBuffer(intbufferIdx, int usage)

    Parcel data, reply;

    data.writeInterfaceToken(ISurface::getInterfaceDescriptor());

    data.writeInt32(bufferIdx);

    data.writeInt32(usage);

    remote()->transact(REQUEST_BUFFER, data, &reply);

    sp<GraphicBuffer> buffer = new GraphicBuffer();

    reply.read(*buffer);//Parcel调用unflatten函数把信息反序列化到这个buffer中。

    return buffer;//requestBuffer实际上返回的是本地new出来的这个GraphicBuffer

status_t GraphicBuffer::flatten(void* buffer,size_t size,

       int fds[], size_t count) const

    //buffer是装载数据的缓冲区，由Parcel提供

     ......

    if(handle) {

       buf[6] = handle->numFds;

       buf[7] = handle->numInts;

       native_handle_t const* const h = handle;

       //把handle的信息也写到buffer中

       memcpy(fds,     h->data,             h->numFds*sizeof(int));

       memcpy(&buf[8], h->data + h->numFds,h->numInts*sizeof(int));

    returnNO_ERROR;

status_t GraphicBuffer::unflatten(void const*buffer, size_t size,

       int fds[], size_t count)

        ......

    if(numFds || numInts) {

       width  = buf[1];

       height = buf[2];

       stride = buf[3];

       format = buf[4];

       usage  = buf[5];

        native_handle* h =native_handle_create(numFds, numInts);

       memcpy(h->data,         fds,     numFds*sizeof(int));

        memcpy(h->data + numFds, &buf[8],numInts*sizeof(int));

       handle = h;//根据Parcel包中的数据还原一个handle

    } else{

       width = height = stride = format = usage = 0;

       handle = NULL;

    mOwner= ownHandle;

    returnNO_ERROR;

status_tsw_gralloc_handle_t::registerBuffer(sw_gralloc_handle_t* hnd)

if (hnd->pid != getpid()) {

        //原来是做一次内存映射操作

       void* base = mmap(0, hnd->size, hnd->prot, MAP_SHARED, hnd->fd,0);

        ......

       //base保存着共享内存的起始地址

       hnd->base = intptr_t(base);

    returnNO_ERROR;

//lock操作

int sw_gralloc_handle_t::lock(sw_gralloc_handle_t*hnd, int usage,

       int l, int t, int w, int h, void** vaddr)

    *vaddr= (void*)hnd->base;//得到共享内存的起始地址，后续作画就使用这块内存了。

    returnNO_ERROR;

//unlock操作

status_tsw_gralloc_handle_t::unlock(sw_gralloc_handle_t* hnd)

    returnNO_ERROR;//没有任何操作

void SurfaceFlinger::instantiate() {

   defaultServiceManager()->addService(

           String16("SurfaceFlinger"), new SurfaceFlinger());

class SurfaceFlinger : public BnSurfaceComposer,protected Thread

SurfaceFlinger::SurfaceFlinger()

    :   BnSurfaceComposer(), Thread(false),

       mTransactionFlags(0),

       mTransactionCount(0),

       mResizeTransationPending(false),

       mLayersRemoved(false),

       mBootTime(systemTime()),

       mHardwareTest("android.permission.HARDWARE_TEST"),

       mAccessSurfaceFlinger("android.permission.ACCESS_SURFACE_FLINGER"),

       mDump("android.permission.DUMP"),

       mVisibleRegionsDirty(false),

       mDeferReleaseConsole(false),

       mFreezeDisplay(false),

        mFreezeCount(0),

       mFreezeDisplayTime(0),

       mDebugRegion(0),

       mDebugBackground(0),

       mDebugInSwapBuffers(0),

       mLastSwapBufferTime(0),

       mDebugInTransaction(0),

       mLastTransactionTime(0),

       mBootFinished(false),

       mConsoleSignals(0),

       mSecureFrameBuffer(0)

   init();//上面没有调用run。必须到init去检查一番。

//init函数更简单了。

void SurfaceFlinger::init()

    charvalue[PROPERTY_VALUE_MAX];

   property_get("debug.sf.showupdates", value, "0");

   mDebugRegion = atoi(value);

   property_get("debug.sf.showbackground", value, "0");

   mDebugBackground = atoi(value);

void SurfaceFlinger::onFirstRef()

//真是梦里寻他千百度，果然是在onFirstRef中创建了工作线程

run("SurfaceFlinger",PRIORITY_URGENT_DISPLAY);

mReadyToRunBarrier类型为Barrier，这个类就是封装了一个Mutex对象和一个Condition

对象。如果读者还记得第5章有关同步类的介绍，理解这个Barrier就非常简单了。下面调用的

wait函数表示要等待一个同步条件的满足。

    mReadyToRunBarrier.wait();

不清楚Thread类的读者可以复习一下与第5章有关的Thread类的知识。

status_t SurfaceFlinger::readyToRun()

    intdpy = 0;

        //①GraphicPlane是什么？

       GraphicPlane& plane(graphicPlane(dpy));

        //②为这个GraphicPlane设置一个HAL对象——DisplayHardware

       DisplayHardware* const hw = new DisplayHardware(this, dpy);

       plane.setDisplayHardware(hw);

 //创建Surface系统中的“CB”对象，按照老规矩，应该先创建一块共享内存，然后使用placment new

   mServerHeap = new MemoryHeapBase(4096,

                            MemoryHeapBase::READ_ONLY,

                            "SurfaceFlingerread-only heap");

注意这个“CB“对象的类型是surface_flinger_cblk_t。为什么在CB上打引号呢？因为这个对象

谈不上什么控制，只不过被用来存储一些信息罢了。其控制作用完全达不到audio_track_cblk_t

的程度。基于这样的事实，我们把前面提到的SharedBuffer家族称之为CB对象。

   mServerCblk=

      static_cast<surface_flinger_cblk_t*>(mServerHeap->getBase());

   //placementnew创建surface_flinger_cblk_t

   new(mServerCblk) surface_flinger_cblk_t;

    constGraphicPlane& plane(graphicPlane(dpy));

    constDisplayHardware& hw = plane.displayHardware();

    constuint32_t w = hw.getWidth();

    constuint32_t h = hw.getHeight();

    constuint32_t f = hw.getFormat();

   hw.makeCurrent();

    //当前只有一块屏

    mServerCblk->connected|= 1<<dpy;

    //屏幕在“CB”对象中的代表是display_cblk_t

   display_cblk_t* dcblk = mServerCblk->displays + dpy;

   memset(dcblk, 0, sizeof(display_cblk_t));

   dcblk->w            =plane.getWidth();

   dcblk->h            =plane.getHeight();

    ......//获取屏幕信息

   //还用上了内联汇编语句。

   asmvolatile ("":::"memory");

   下面是一些和OpenGL相关的函数调用。读者如感兴趣，可以研究一下，

   至少SurfaceFlinger.cpp中所涉及的相关代码还不算难懂

   glActiveTexture(GL_TEXTURE0);

   glBindTexture(GL_TEXTURE_2D, 0);

   ......

   glOrthof(0, w, h, 0, 0, 1);

   //LayerDim是Dim类型的Layer

  LayerDim::initDimmer(this, w, h);

    //还记得在onFirstRef函数中的wait吗？下面的open将触发这个同步条件

    mReadyToRunBarrier.open();

    //资源准备好后，init将启动bootanim程序，这样就见到开机动画了。

   property_set("ctl.start", "bootanim");

    returnNO_ERROR;

GraphicPlane     mGraphicPlanes[1];

DisplayHardware::DisplayHardware(

       const sp<SurfaceFlinger>& flinger,

       uint32_t dpy)

    :DisplayHardwareBase(flinger, dpy)

   init(dpy); //最重要的是这个init函数。

void DisplayHardware::init(uint32_t dpy)

//FrameBufferNativeWindow实现了对FrameBuffer的管理和操作，该类中创建了两个

//FrameBuffer，分别起到FrontBuffer和BackBuffer的作用。

mNativeWindow = new FramebufferNativeWindow();

   framebuffer_device_t const * fbDev = mNativeWindow->getDevice();

   mOverlayEngine = NULL;

   hw_module_t const* module;//Overlay相关

    if(hw_get_module(OVERLAY_HARDWARE_MODULE_ID, &module) == 0) {

       overlay_control_open(module, &mOverlayEngine);

......

    EGLint w, h, dummy;

    EGLintnumConfigs=0;

   EGLSurface surface;

   EGLContext context;

    mFlags= CACHED_BUFFERS;

  //EGLDisplay在EGL中代表屏幕

   EGLDisplay display = eglGetDisplay(EGL_DEFAULT_DISPLAY);

    ......

    surface是EGLSurface类型，下面这个函数会将EGL和Android中的Display系统绑定起来，

    后续就可以利用OpenGL在这个Surface上绘画，然后通过eglSwappBuffers输出图像了。

    surface= eglCreateWindowSurface(display, config,

    mNativeWindow.get(),NULL);

   ......

   mDisplay = display;

   mConfig  = config;

   mSurface = surface;

   mContext = context;

   mFormat  = fbDev->format;

   mPageFlipCount = 0;

本节的内容，实际上涉及另外一个比Surface更复杂的Display系统，出于篇幅和精力的原因，本书目前不打算讨论它。

bool SurfaceFlinger::threadLoop()

   waitForEvent();//① 等待什么事件呢？

   if (UNLIKELY(mConsoleSignals)) {

       handleConsoleEvents();

    if(LIKELY(mTransactionCount == 0)) {

      const uint32_t mask = eTransactionNeeded | eTraversalNeeded;

       uint32_t transactionFlags = getTransactionFlags(mask);

        if(LIKELY(transactionFlags)) {

            //Transaction（事务）处理，放到本节最后来讨论

           handleTransaction(transactionFlags);

    //②处理PageFlipping工作

   handlePageFlip();

    constDisplayHardware& hw(graphicPlane(0).displayHardware());

if (LIKELY(hw.canDraw() && !isFrozen())) {

        //③处理重绘

        handleRepaint();

        hw.compositionComplete();

        //④投递BackBuffer

       unlockClients();

        postFramebuffer();

    } else{

       unlockClients();

       usleep(16667);

    returntrue;

void SurfaceFlinger::waitForEvent()

    while(true) {

       nsecs_t timeout = -1;

       const nsecs_t freezeDisplayTimeout = ms2ns(5000);

        ......

       MessageList::value_type msg = mEventQueue.waitMessage(timeout);

        ......//还有一些和冻屏相关的内容

        if(msg != 0) {

           switch (msg->what) {

//千辛万苦就等这一个重绘消息

               case MessageQueue::INVALIDATE:

                     return;

void SurfaceFlinger::signal() const {

    const_cast<SurfaceFlinger*>(this)->signalEvent();

void SurfaceFlinger::signalEvent() {

   mEventQueue.invalidate(); //往消息队列中加入INVALIDATE消息

注意：事务处理将在8.5.3节中介绍。

void SurfaceFlinger::handlePageFlip()

bool visibleRegions = mVisibleRegionsDirty;

还记得前面所说的mCurrentState吗？它保存了所有显示层的信息，而绘制的时候使用的

mDrawingState则保存了当前需要显示的显示层信息。

LayerVector& currentLayers =

                 const_cast<LayerVector&>(mDrawingState.layersSortedByZ);

//①调用lockPageFlip

visibleRegions |= lockPageFlip(currentLayers);

const DisplayHardware& hw =graphicPlane(0).displayHardware();

//取得屏幕的区域

const Region screenRegion(hw.bounds());

if (visibleRegions) {

     Region opaqueRegion;

     computeVisibleRegions(currentLayers, mDirtyRegion,opaqueRegion);

     mWormholeRegion = screenRegion.subtract(opaqueRegion);

     mVisibleRegionsDirty = false;

//② 调用unlockPageFlip

unlockPageFlip(currentLayers);

mDirtyRegion.andSelf(screenRegion);

bool SurfaceFlinger::lockPageFlip(constLayerVector& currentLayers)

    boolrecomputeVisibleRegions = false;

    size_tcount = currentLayers.size();

   sp<LayerBase> const* layers = currentLayers.array();

    for(size_t i=0 ; i<count ; i++) {

       const sp<LayerBase>& layer = layers[i];

        //调用每个显示层的lockPageFlip

       layer->lockPageFlip(recomputeVisibleRegions);

    returnrecomputeVisibleRegions;

void Layer::lockPageFlip(bool&recomputeVisibleRegions)

  //lcblk是SharedBufferServer类型，调用retireAndLock函数将返回FrontBuffer的

  //索引号

    ssize_tbuf = lcblk->retireAndLock();

    ......

   mFrontBufferIndex = buf;

    //得到FrontBuffer对应的GraphicBuffer

   sp<GraphicBuffer> newFrontBuffer(getBuffer(buf));

if (newFrontBuffer != NULL) {

        //取出脏区域

      const Region dirty(lcblk->getDirtyRegion(buf));

        //和GraphicBuffer所表示的区域进行裁剪，得到一个脏区域

       mPostedDirtyRegion = dirty.intersect( newFrontBuffer->getBounds() );

       const Layer::State& front(drawingState());

        if(newFrontBuffer->getWidth()  ==front.requested_w &&

            newFrontBuffer->getHeight() ==front.requested_h)

           if ((front.w != front.requested_w) ||

               (front.h != front.requested_h))

               ...... //需要重新计算可见区域

               recomputeVisibleRegions = true;

           mFreezeLock.clear();

    } else{

       mPostedDirtyRegion.clear();

    if(lcblk->getQueuedCount()) {

       mFlinger->signalEvent();

如果脏区域不为空，则需要绘制成纹理，reloadTexture将绘制一张纹理保存在

mTextures数组中，里边涉及很多OpenGL的操作，读者有兴趣可以自己研究。

    if(!mPostedDirtyRegion.isEmpty()) {

       reloadTexture( mPostedDirtyRegion );

void SurfaceFlinger::unlockPageFlip(constLayerVector& currentLayers)

     constGraphicPlane& plane(graphicPlane(0));

    constTransform& planeTransform(plane.transform());

    size_tcount = currentLayers.size();

   sp<LayerBase> const* layers = currentLayers.array();

    for(size_t i=0 ; i<count ; i++) {

       const sp<LayerBase>& layer = layers[i];

        //调用每个显示层的unlockPageFlip，Layer的unlockPageFlip主要做一些

//区域的清理工作，读者可以自己看看。

       layer->unlockPageFlip(planeTransform, mDirtyRegion);

void SurfaceFlinger::handleRepaint()

    mInvalidRegion.orSelf(mDirtyRegion);

    if(mInvalidRegion.isEmpty()) {

       return;

    ......

    constDisplayHardware& hw(graphicPlane(0).displayHardware());

   glMatrixMode(GL_MODELVIEW);

   glLoadIdentity();

   uint32_t flags = hw.getFlags();

    if((flags & DisplayHardware::SWAP_RECTANGLE) ||

       (flags & DisplayHardware::BUFFER_PRESERVED))

        ......//计算mDirtyRegion

    // 在脏区域上进行绘制

   composeSurfaces(mDirtyRegion);

   mDirtyRegion.clear();

void SurfaceFlinger::composeSurfaces(constRegion& dirty)

    constSurfaceFlinger& flinger(*this);

    constLayerVector& drawingLayers(mDrawingState.layersSortedByZ);

    constsize_t count = drawingLayers.size();

   sp<LayerBase> const* const layers = drawingLayers.array();

    for(size_t i=0 ; i<count ; ++i) {

       const sp<LayerBase>& layer = layers[i];

        const Region&visibleRegion(layer->visibleRegionScreen);

        if(!visibleRegion.isEmpty())  {

           const Region clip(dirty.intersect(visibleRegion));

           if (!clip.isEmpty()) {

               layer->draw(clip); //调用各个显示层的layer函数

void LayerBase::draw(const Region& inClip)const

    ......

    glEnable(GL_SCISSOR_TEST);

   onDraw(clip);//调用子类的onDraw函数

void Layer::onDraw(const Region& clip) const

    intindex = mFrontBufferIndex;

    if(mTextures[index].image == EGL_NO_IMAGE_KHR)

       index = 0;

        GLuint textureName = mTextures[index].name;

       Region holes(clip.subtract(under));

        if(!holes.isEmpty()) {

           clearWithOpenGL(holes);

       return;

//index是FrontBuffer对应生成的纹理，在lockPageFlip函数中就已经生成了。

 drawWithOpenGL(clip,mTextures[index]);//将纹理画上去，里面有很多和OpenGL相关内容

void LayerBase::drawWithOpenGL(const Region&clip, const Texture& texture) const

    constDisplayHardware& hw(graphicPlane(0).displayHardware());

    constuint32_t fbHeight = hw.getHeight();

    constState& s(drawingState());

    //validateTexture函数内部将绑定指定的纹理

   validateTexture(texture.name);

    //下面就是OpenGL操作函数了

   glEnable(GL_TEXTURE_2D);

    ......

   glMatrixMode(GL_TEXTURE);

   glLoadIdentity();

    //坐标旋转

    switch(texture.transform) {

       case HAL_TRANSFORM_ROT_90:

           glTranslatef(0, 1, 0);

           glRotatef(-90, 0, 0, 1);

           break;

       case HAL_TRANSFORM_ROT_180:

           glTranslatef(1, 1, 0);

           glRotatef(-180, 0, 0, 1);

           break;

       case HAL_TRANSFORM_ROT_270:

           glTranslatef(1, 0, 0);

           glRotatef(-270, 0, 0, 1);

           break;

if (texture.NPOTAdjust) {

        //缩放处理

       glScalef(texture.wScale, texture.hScale, 1.0f);

   //使能纹理坐标

glEnableClientState(GL_TEXTURE_COORD_ARRAY);

//设置顶点坐标

glVertexPointer(2, GL_FIXED, 0, mVertices);

//设置纹理坐标

   glTexCoordPointer(2, GL_FIXED, 0, texCoords);

    while(it != end) {

       const Rect& r = *it++;

       const GLint sy = fbHeight - (r.top + r.height());

       glScissor(r.left, sy, r.width(), r.height());

        //画矩形

       glDrawArrays(GL_TRIANGLE_FAN, 0, 4);

//禁止纹理坐标

   glDisableClientState(GL_TEXTURE_COORD_ARRAY);

void LayerBase::validateTexture(GLinttextureName) const

    //下面这个函数将绑定纹理

   glBindTexture(GL_TEXTURE_2D, textureName);

    ......//其他一些设置

我在Android平台上有几个月的OpenGL开发经历，还谈不上很深刻，其中的一些资料，希望能够给感兴趣的读者提供参考。

1）OpenGL的入门教材当选NeHe的资料，大略看前几章即可。

2） Android平台上关于OpenGL ES的开发，有一篇很详细的Word文档叫《OpenGL ESTutorial for Android》。该文详细描述了在Android平台上进行OpenGL开发的流程。大家可跟着这篇教材，在模拟器上做一些练习。那里面涉及到的一些基础知识，从前面介绍的入门教材中可以学到。

3）有了前面两点的基础后，就需要对整个OpenGL有比较完整深入的了解了。我在那时所看的书是《OpenGL Programming Guide (7th Edition)》。该书很厚，有1000多页。里面有一些内容可能与工作无涉，只要大概知道有那回事就行了，暂时不必深入学习，等需要时再进一步学习并运用。我在开发的项目中曾用到的光照、雾化等效果，都是之前先知道有这个东西，后来在项目中才逐渐学习运用的。

4）嵌入式平台上用的其实是OpenGL ES。这里，还有一本书叫《OpenGL ES 2.0 Programming Guide》，它介绍了OpenGL ES的开发，读者可认真修习。

5）在Android SDK文档中，对OpenGL API的描述只寥寥数语。怎么办？由于它使用了J2ME中的javax.microedition.khronos.opengles包，所以J2ME的SDK文档中对OpenGL的API有着非常详细的描述，读者手头应该要有一个J2ME的文档。

6）如果想做深入开发，就不得不学习计算机图形学了。我后来买了书，可惜没时间学了。

void SurfaceFlinger::unlockClients()

    constLayerVector& drawingLayers(mDrawingState.layersSortedByZ);

    constsize_t count = drawingLayers.size();

   sp<LayerBase> const* const layers = drawingLayers.array();

    for (size_t i=0 ; i<count ; ++i) {

       const sp<LayerBase>& layer = layers[i];

       layer->finishPageFlip();

void Layer::finishPageFlip()

    //释放FrontBufferIndex

   status_t err = lcblk->unlock( mFrontBufferIndex );

void SurfaceFlinger::postFramebuffer()

    if(!mInvalidRegion.isEmpty()) {

       const DisplayHardware& hw(graphicPlane(0).displayHardware());

       const nsecs_t now = systemTime();

       mDebugInSwapBuffers = now;

//调用这个函数后，混合后的图像就会传递到屏幕中显示了

       hw.flip(mInvalidRegion);

       mLastSwapBufferTime = systemTime() - now;

       mDebugInSwapBuffers = 0;

       mInvalidRegion.clear();

void DisplayHardware::flip(const Region&dirty) const

   checkGLErrors();

   EGLDisplay dpy = mDisplay;

   EGLSurface surface = mSurface;

......

    if(mFlags & PARTIAL_UPDATES) {

       mNativeWindow->setUpdateRectangle(dirty.getBounds());

   mPageFlipCount++;

   eglSwapBuffers(dpy, surface);//PageFlipping，此后图像终于显示在屏幕上了！

Surface createSurfaceLocked() {            

Surface.openTransaction(); //开始一次transaction

         mSurfaceX = mFrame.left + mXOffset;

          mSurfaceY = mFrame.top + mYOffset;

          //设置Surface的位置

         mSurface.setPosition(mSurfaceX, mSurfaceY);

          ......

       }finally {

             Surface.closeTransaction(); //关闭这次事务

static void Surface_openTransaction(JNIEnv* env,jobject clazz)

    //调用SurfaceComposerClient的openGlobalTransaction函数

SurfaceComposerClient::openGlobalTransaction();

voidSurfaceComposerClient::openGlobalTransaction()

   Mutex::Autolock _l(gLock);

    ......

    constsize_t N = gActiveConnections.size();

    for(size_t i=0; i<N; i++) {

        sp<SurfaceComposerClient>client(gActiveConnections.valueAt(i).promote());

        //gOpenTransactions存储当前提交事务请求的Client

        if(client != 0 && gOpenTransactions.indexOf(client) < 0) {

           //Client是保存在全局变量gActiveConnections中的SurfaceComposerClient

            //对象，调用它的openTransaction。

           if (client->openTransaction() == NO_ERROR) {

               if (gOpenTransactions.add(client) < 0) {

                   client->closeTransaction();

           ......

status_tSurfaceComposerClient::openTransaction()

    if(mStatus != NO_ERROR)

       return mStatus;

   Mutex::Autolock _l(mLock);

    mTransactionOpen++; //一个计数值，用来控制事务的提交。

    if(mPrebuiltLayerState == 0) {

       mPrebuiltLayerState = new layer_state_t;

    returnNO_ERROR;

static void Surface_setPosition(JNIEnv* env,jobject clazz, jint x, jint y)

    constsp<SurfaceControl>& surface(getSurfaceControl(env, clazz));

    if(surface == 0) return;

   status_t err = surface->setPosition(x, y);

status_t SurfaceControl::setPosition(int32_t x,int32_t y) {

    constsp<SurfaceComposerClient>& client(mClient);

   status_t err = validate();

if (err < 0) return err;

//调用SurfaceComposerClient的setPosition函数

    returnclient->setPosition(mToken, x, y);

status_tSurfaceComposerClient::setPosition(SurfaceID id, int32_t x, int32_t y)

   layer_state_t* s = _lockLayerState(id); //找到对应的layer_state_t

    if(!s) return BAD_INDEX;

   s->what |= ISurfaceComposer::ePositionChanged;

   s->x = x;

   s->y = y;  //上面几句修改了这块layer的参数

   _unlockLayerState(); //该函数将unlock一个同步对象，其他没有做什么工作

    returnNO_ERROR;

static void Surface_closeTransaction(JNIEnv*env, jobject clazz)

   SurfaceComposerClient::closeGlobalTransaction();

voidSurfaceComposerClient::closeGlobalTransaction()

......

const size_t N = clients.size();

sp<ISurfaceComposer>sm(getComposerService());

//①先调用SF的openGlobalTransaction

sm->openGlobalTransaction();

for (size_t i=0; i<N; i++) {

   //②然后调用每个SurfaceComposerClient对象的closeTransaction

   clients[i]->closeTransaction();

//③最后调用SF的closeGlobalTransaction

sm->closeGlobalTransaction();

void SurfaceFlinger::openGlobalTransaction()

   android_atomic_inc(&mTransactionCount);//又是一个计数控制

status_tSurfaceComposerClient::closeTransaction()

    if(mStatus != NO_ERROR)

       return mStatus;

   Mutex::Autolock _l(mLock);

   ......

    constssize_t count = mStates.size();

if (count) {

     //mStates是这个SurfaceComposerClient中保存的所有layer_state_t数组，也就是

    //每个Surface一个。然后调用跨进程的setState

       mClient->setState(count, mStates.array());

       mStates.clear();

    returnNO_ERROR;

status_t SurfaceFlinger::setClientState(ClientIDcid, int32_t count,

                          const layer_state_t*states)

   Mutex::Autolock _l(mStateLock);

   uint32_t flags = 0;

    cid<<= 16;

    for(int i=0 ; i<count ; i++) {

       const layer_state_t& s = states[i];

       sp<LayerBaseClient> layer(getLayerUser_l(s.surface | cid));

        if(layer != 0) {

           const uint32_t what = s.what;

           if (what & ePositionChanged) {

               if (layer->setPosition(s.x, s.y))

                    //eTraversalNeeded表示需要遍历所有显示层

                    flags |= eTraversalNeeded;

    if(flags) {

       setTransactionFlags(flags);//这里将会触发threadLoop的事件。

    returnNO_ERROR;

uint32_tSurfaceFlinger::setTransactionFlags(uint32_t flags, nsecs_t delay)

   uint32_t old = android_atomic_or(flags, &mTransactionFlags);

    if((old & flags)==0) {

        if(delay > 0) {

           signalDelayedEvent(delay);

        }else {

            signalEvent();  //设置完mTransactionFlags后，触发事件。

    returnold;

void SurfaceFlinger::closeGlobalTransaction()

if (android_atomic_dec(&mTransactionCount) ==1) {

//注意下面语句的执行条件，当mTransactionCount变为零时才执行，这意味着

//openGlobalTransaction两次的话，只有最后一个closeGlobalTransaction调用

//才会真正地提交事务

       signalEvent();

       Mutex::Autolock _l(mStateLock);

       //如果这次事务涉及尺寸调整，则需要等一段时间

       while (mResizeTransationPending) {

           status_t err = mTransactionCV.waitRelative(mStateLock, s2ns(5));

           if (CC_UNLIKELY(err != NO_ERROR)) {

               mResizeTransationPending = false;

               break;

bool SurfaceFlinger::threadLoop()

   waitForEvent();

    if(LIKELY(mTransactionCount == 0)) {

     const uint32_t mask = eTransactionNeeded | eTraversalNeeded;

      uint32_ttransactionFlags = getTransactionFlags(mask);

        if(LIKELY(transactionFlags)) {

           handleTransaction(transactionFlags);

uint32_t SurfaceFlinger::getTransactionFlags(uint32_tflags)

//先通过原子操作去掉mTransactionFlags中对应的位。

//而后原子操作返回的旧值和flags进行与操作

return android_atomic_and(~flags,&mTransactionFlags) & flags;

void SurfaceFlinger::handleTransaction(uint32_ttransactionFlags)

   Vector< sp<LayerBase> > ditchedLayers;

       Mutex::Autolock _l(mStateLock);

        //调用handleTransactionLocked函数处理

       handleTransactionLocked(transactionFlags, ditchedLayers);

    constsize_t count = ditchedLayers.size();

    for(size_t i=0 ; i<count ; i++) {

        if(ditchedLayers[i] != 0) {

        //ditch是丢弃的意思，有些显示层可能被hide了，所以这里做些收尾的工作

          ditchedLayers[i]->ditch();

void SurfaceFlinger::handleTransactionLocked(

       uint32_t transactionFlags, Vector< sp<LayerBase> >&ditchedLayers)

    //这里使用了mCurrentState，它的layersSortedByZ数组存储了SF中所有的显示层

    constLayerVector& currentLayers(mCurrentState.layersSortedByZ);

    constsize_t count = currentLayers.size();

     constbool layersNeedTransaction = transactionFlags & eTraversalNeeded;

     //如果需要遍历所有显示的话。

    if(layersNeedTransaction) {

       for (size_t i=0 ; i<count ; i++) {

           const sp<LayerBase>& layer = currentLayers[i];

           uint32_t trFlags = layer->getTransactionFlags(eTransactionNeeded);

           if (!trFlags) continue;

           //调用各个显示层的doTransaction函数。

            constuint32_t flags = layer->doTransaction(0);

           if (flags & Layer::eVisibleRegion)

               mVisibleRegionsDirty = true;

    if(transactionFlags & eTransactionNeeded) {

        if(mCurrentState.orientation != mDrawingState.orientation) {

         //横竖屏如果发生切换，需要对应变换设置。

           const int dpy = 0;

           const int orientation = mCurrentState.orientation;

           const uint32_t type = mCurrentState.orientationType;

           GraphicPlane& plane(graphicPlane(dpy));

           plane.setOrientation(orientation);

           ......

      mLayersRemoved变量在显示层被移除的时候设置，例如removeLayer函数，这些函数

      也会触发handleTranscation函数的执行

      if(mLayersRemoved) {

           mLayersRemoved = false;

           mVisibleRegionsDirty = true;

           const LayerVector& previousLayers(mDrawingState.layersSortedByZ);

           const size_t count = previousLayers.size();

           for (size_t i=0 ; i<count ; i++) {

               const sp<LayerBase>& layer(previousLayers[i]);

               if (currentLayers.indexOf( layer ) < 0) {

                  ditchedLayers.add(layer);

                   mDirtyRegionRemovedLayer.orSelf(layer->visibleRegionScreen);

       free_resources_l();

    //提交事务处理，有必要进去看看。

   commitTransaction();

void SurfaceFlinger::commitTransaction()

   //mDrawingState将使用更新后的mCurrentState

   mDrawingState = mCurrentState;

mResizeTransationPending = false;

//触发一个条件变量，这样等待在closeGlobalTransaction函数中的线程可以放心地返回了。

   mTransactionCV.broadcast();

class SharedBufferStack{

 ......

虽然PageFlipping使用Front和Back两个Buffer就可以了，但是SBT的结构和相关算法

是支持多个缓冲的。另外，缓冲是按照块来获取的，也就是一次获得一块缓冲，每块缓冲用

一个编号表示（这一点在之前的分析已经介绍过了）。

int32_t head;      

 int32_tavailable; //当前可用的空闲缓冲个数

  int32_t queued;    //SBC投递的脏缓冲个数

  int32_tinUse;  //SBS当前正在使用的缓冲编号

  ......//上面这几个参数联合SBC中的tail，我称之为控制参数。

SharedBufferServer::SharedBufferServer(SharedClient*sharedClient,

       int surface, int num, int32_t identity)

    :SharedBufferBase(sharedClient, surface, num, identity)

mSharedStack->init(identity);//这个函数将设置inUse为-1

//下面设置SBT中的参数，我们关注前三个

   mSharedStack->head = num-1;

    mSharedStack->available = num;

mSharedStack->queued = 0;

//设置完后，head=2-1=1,available=2,queued=0，inUse=-1

   mSharedStack->reallocMask = 0;

   memset(mSharedStack->dirtyRegion, 0,sizeof(mSharedStack->dirtyRegion));

SharedBufferClient::SharedBufferClient(SharedClient*sharedClient,

       int surface, int num, int32_t identity)

    :SharedBufferBase(sharedClient, surface, num, identity), tail(0)

    tail =computeTail(); //tail是SBC定义的变量，注意它不是SBT定义的。

int32_t SharedBufferClient::computeTail() const

   SharedBufferStack& stack( *mSharedStack );

   int32_t newTail;

   int32_t avail;

   int32_t head;

       avail = stack.available; //available=2,head=1

       head = stack.head;

    }while (stack.available != avail);

   newTail = head - avail + 1;//newTail=1-2+1=0

    if(newTail < 0) {

       newTail += mNumBuffers;

    } elseif (newTail >= mNumBuffers) {

       newTail -= mNumBuffers;

    return newTail;//计算得到newTail=0

ssize_t SharedBufferClient::dequeue()

   SharedBufferStack& stack( *mSharedStack );

......

//DequeueCondition函数对象

   DequeueCondition condition(this);

status_t err = waitForCondition(condition);

//成功以后，available减1，表示当前可用的空闲buffer只有1个

if (android_atomic_dec(&stack.available) == 0) {

    ......

int dequeued = tail; //tail值为0，所以dequeued的值为0。

//tail加1。如果超过2，则重新置为0，这表明tail的值在0,1间循环。

    tail =((tail+1 >= mNumBuffers) ? 0 : tail+1);

......

//返回的这个dequeued值为零，也就是tail加1操作前的旧值。这一点请读者务必注意。

    returndequeued;

bool SharedBufferClient::DequeueCondition::operator()(){

    returnstack.available > 0;//只要available大于0就算满足条件，第一次进来肯定满足

status_t SharedBufferClient::lock(int buf)

   LockCondition condition(this, buf);

    status_terr = waitForCondition(condition);

    returnerr;

boolSharedBufferClient::LockCondition::operator()() {

这个条件其实就是判断编号为buf的Buffer是不是被使用了。

buf值为0，head值为1，queued为0，inUse为-1

    return(buf != stack.head ||

            (stack.queued > 0 && stack.inUse!= buf));

status_t SharedBufferClient::queue(int buf)

   QueueUpdate update(this);

   status_t err = updateCondition( update );

    ......

    returnerr;

//直接看这个QueueUpdate函数对象

ssize_tSharedBufferClient::QueueUpdate::operator()() {

   android_atomic_inc(&stack.queued);//queued增加1，现在该值由零变为1

    returnNO_ERROR;

ssize_t SharedBufferServer::retireAndLock()

   RetireUpdate update(this, mNumBuffers);

   ssize_t buf = updateCondition( update );

    returnbuf;

ssize_tSharedBufferServer::RetireUpdate::operator()() {

    //先取得head值，为1

   int32_t head = stack.head;

    //inUse被设置为1。表明要使用1吗？目前的脏缓冲应该是0才对

   android_atomic_write(head, &stack.inUse);

   int32_tqueued;

       queued = stack.queued; //queued目前为1

        if(queued == 0) {

           return NOT_ENOUGH_DATA;

      //下面这个原子操作使得stack.queued减1.

    }while (android_atomic_cmpxchg(queued, queued-1, &stack.queued));

    //while循环退出后，queued减1，又变为0。

    //head值也在0,1间循环，现在head值变为0了

    head =((head+1 >= numBuffers) ? 0 : head+1);

    //inUse被设置为0

   android_atomic_write(head, &stack.inUse);

    // head值被设为0

   android_atomic_write(head, &stack.head);

    // available加1，变成2.

    android_atomic_inc(&stack.available);

    returnhead;//返回0

ssize_tSharedBufferServer::UnlockUpdate::operator()() {

    ......

   android_atomic_write(-1, &stack.inUse);//inUse被设置为-1

    returnNO_ERROR;

像下面这样的代码，如果有锁控制的话根本用不着一个while循环，因为有锁的保护，没有其他线程

能够修改stack.queued的值，所以用while来循环判断android_atomic_cmpxchg没有什么意义。

   int32_tqueued;

       queued = stack.queued;

        if(queued == 0) {

           return NOT_ENOUGH_DATA;

    }while (android_atomic_cmpxchg(queued, queued-1, &stack.queued));

为什么我对生产/消费的同步控制如此感兴趣呢？这和自己工作的经历有些关系。因为之前曾做过一个单写多读的跨进程缓冲类，也就是一个生产者，多个消费者。为了保证正确性和一定的效率，我们在算法上曾做了很多改进，但还是大量使用了锁，所以我很好奇Google是怎么做到的，这也体现了一个高手的内功修养。要是由读者自己来实现，结果会怎样呢？

sp<LayerBaseClient> SurfaceFlinger::createPushBuffersSurfaceLocked(

       const sp<Client>& client, DisplayID display,

       int32_t id, uint32_t w, uint32_t h, uint32_t flags)

   sp<LayerBuffer> layer = new LayerBuffer(this, display, client,id);

   layer->initStates(w, h, flags);

   addLayer_l(layer);

    returnlayer;

status_tCameraService::Client::registerPreviewBuffers()

    int w, h;

   CameraParameters params(mHardware->getParameters());

   params.getPreviewSize(&w, &h);

    ①mHardware代表Camera设备的HAL对象。本书讨论CameraHardwareStub设备，它其实是

   一个虚拟的设备，不过其代码却具有参考价值。

   BufferHeap定义为ISurface的内部类，其实就是对IMemoryHeap的封装

   ISurface::BufferHeapbuffers(w, h, w, h,

                                HAL_PIXEL_FORMAT_YCrCb_420_SP,

                                 mOrientation,

                                mHardware->getPreviewHeap());

    //②调用SurfaceLayerBuffer的registerBuffers函数。

   status_t ret = mSurface->registerBuffers(buffers);

    returnret;

 classBufferHeap {

   public:

       ......

        //使用这个构造函数

       BufferHeap(uint32_t w, uint32_t h,

               int32_t hor_stride, int32_t ver_stride,

               PixelFormat format, const sp<IMemoryHeap>& heap);

      ......

       ~BufferHeap();

       uint32_t w;

       uint32_t h;

       int32_t hor_stride;

       int32_t ver_stride;

       PixelFormat format;

       uint32_t transform;

       uint32_t flags;

       sp<IMemoryHeap> heap; //heap指向真实的存储对象

sp<IMemoryHeap>CameraHardwareStub::getPreviewHeap() const

    returnmPreviewHeap;//返回一个成员变量，它又是在哪创建的呢？

//上面的mPreivewHeap对象由initHeapLocked函数创建，该函数在HAL对象创建的时候被调用

void CameraHardwareStub::initHeapLocked()

  ......

创建一个MemoryHeapBase对象，大小是mPreviewFrameSize * kBufferCount,其中

 kBufferCount为4。注意这是一段连续的缓冲。

 mPreviewHeap= new MemoryHeapBase(mPreviewFrameSize * kBufferCount);

 //mBuffer为MemoryBase数组，元素为4

 for (inti = 0; i < kBufferCount; i++) {

       mBuffers[i] = new MemoryBase(mPreviewHeap,

i * mPreviewFrameSize, mPreviewFrameSize);

status_t LayerBuffer::SurfaceLayerBuffer::registerBuffers(

       const ISurface::BufferHeap& buffers)

   sp<LayerBuffer> owner(getOwner());

if (owner != 0)

      //调用外部类对象的registerBuffers，所以SurfaceLayerBuffer也是一个Proxy哦。

       return owner->registerBuffers(buffers);

    returnNO_INIT;

//外部类是LayerBuffer，调用它的registerBuffers函数

status_t LayerBuffer::registerBuffers(constISurface::BufferHeap& buffers)

Mutex::Autolock _l(mLock);

//创建数据的来源BufferSource，注意我们其实把MemoryHeap设置上去了

   sp<BufferSource> source = new BufferSource(*this, buffers);

   status_t result = source->getStatus();

    if(result == NO_ERROR) {

       mSource = source;//保存这个数据源为mSource。

    returnresult;

//preview线程从Thread类派生，下面这个函数在threadLoop中循环调用

int CameraHardwareStub::previewThread()

mLock.lock();

//每次进来mCurrentPreviewFrame都会加1

   ssize_t offset = mCurrentPreviewFrame * mPreviewFrameSize;

  sp<MemoryHeapBase> heap = mPreviewHeap;

  FakeCamera* fakeCamera = mFakeCamera;//虚拟的摄像机设备

   //从mBuffers中取一块内存，用于接收来自硬件的数据

   sp<MemoryBase>buffer = mBuffers[mCurrentPreviewFrame];

   mLock.unlock();

   if(buffer != 0) {

       intdelay = (int)(1000000.0f / float(previewFrameRate));

      void *base = heap->base();//base是mPreviewHeap的起始位置

        //下面这个frame代表buffer在mPreviewHeap中的起始位置，还记得图8-31吗？

       //四块MemoryBase的起始位置由下面这个代码计算得来

       uint8_t *frame = ((uint8_t *)base) + offset;

        //取出一帧数据，放到对应的MemoryBase中

       fakeCamera->getNextFrameAsYuv422(frame);

        //①把含有帧数据的buffer传递到上层

        if(mMsgEnabled & CAMERA_MSG_PREVIEW_FRAME)

           mDataCb(CAMERA_MSG_PREVIEW_FRAME, buffer, mCallbackCookie);

       //mCurrentPreviewFrame 递增，在0到3之间循环

       mCurrentPreviewFrame = (mCurrentPreviewFrame + 1) % kBufferCount;

       usleep(delay);//模拟真实硬件的延时

    returnNO_ERROR;

voidCameraService::Client::handlePreviewData(const sp<IMemory>& mem)

   ssize_t offset;

size_t size;

//注意传入的mem参数，它实际上是Camera HAL创建的mBuffers数组中的一个

//offset返回的是这个数组在mPreviewHeap中的偏移量

   sp<IMemoryHeap> heap = mem->getMemory(&offset, &size);

    if (!mUseOverlay)

       Mutex::Autolock surfaceLock(mSurfaceLock);

        if(mSurface != NULL) {

           //调用ISurface的postBuffer，注意我们传入的参数是offset。

           mSurface->postBuffer(offset);

......

void LayerBuffer::postBuffer(ssize_t offset)

   sp<Source> source(getSource());//getSource返回mSource，为BufferSource类型

    if(source != 0)

       source->postBuffer(offset);//调用BufferSource的postBuffer函数。

voidLayerBuffer::BufferSource::postBuffer(ssize_t offset)

   ISurface::BufferHeap buffers;

       Mutex::Autolock _l(mBufferSourceLock);

       buffers = mBufferHeap;//还记得图8-32吗？

        if(buffers.heap != 0) {

           //BufferHeap的heap变量指向MemoryHeap,下面取出它的大小

           const size_t memorySize = buffers.heap->getSize();

          //做一下检查，判断这个offset是不是有问题

           if ((size_t(offset) + mBufferSize) > memorySize) {

               LOGE("LayerBuffer::BufferSource::postBuffer() "

                     "invalid buffer(offset=%d, size=%d, heap-size=%d",

                     int(offset),int(mBufferSize), int(memorySize));

               return;

   sp<Buffer> buffer;

if (buffers.heap != 0) {

    //创建一个LayerBuffer::Buffer

       buffer = new LayerBuffer::Buffer(buffers, offset, mBufferSize);

        if(buffer->getStatus() != NO_ERROR)

           buffer.clear();

       setBuffer(buffer);//setBuffer？我们要看看

//mLayer就是外部类LayerBuffer，调用它的invalidate函数将触发SF的重绘

       mLayer.invalidate();

void LayerBuffer::BufferSource::setBuffer(

const sp<LayerBuffer::Buffer>& buffer)

  //setBuffer函数就是简单地将new出来的Buffer设置给成员变量mBuffer，这么做会有问题吗？Mutex::Autolock_l(mBufferSourceLock);

   mBuffer = buffer; //将新的buffer设置为mBuffer，mBuffer原来指向的那个被delete

LayerBuffer::Buffer::Buffer(constISurface::BufferHeap& buffers,

       ssize_t offset, size_t bufferSize)

    :mBufferHeap(buffers), mSupportsCopybit(false)

   //注意，这个src被定义为引用，所以修改src的信息相当于修改mNativeBuffer的信息

   NativeBuffer& src(mNativeBuffer);

   src.crop.l = 0;

   src.crop.t = 0;

   src.crop.r = buffers.w;

   src.crop.b = buffers.h;

   src.img.w       =buffers.hor_stride ?: buffers.w;

   src.img.h       =buffers.ver_stride ?: buffers.h;

    src.img.format  = buffers.format;

    //这个base将指向对应的内存起始地址

   src.img.base    =(void*)(intptr_t(buffers.heap->base()) + offset);

    src.img.handle  = 0;

    gralloc_module_tconst * module = LayerBuffer::getGrallocModule();

    //做一些处理，有兴趣的读者可以去看看。

    if(module && module->perform) {

       int err = module->perform(module,

               GRALLOC_MODULE_PERFORM_CREATE_HANDLE_FROM_BUFFER,

               buffers.heap->heapID(), bufferSize,

               offset, buffers.heap->base(),

                &src.img.handle);

       mSupportsCopybit = (err == NO_ERROR);

void LayerBuffer::onDraw(const Region& clip)const

   sp<Source> source(getSource());

    if(LIKELY(source != 0)) {

       source->onDraw(clip);//source实际类型是BufferSource，我们去看看。

    } else{

       clearWithOpenGL(clip);

void LayerBuffer::BufferSource::onDraw(constRegion& clip) const

   sp<Buffer> ourBuffer(getBuffer());

    ......//使用这个Buffer，注意使用的时候没有锁控制

    mLayer.drawWithOpenGL(clip, mTexture);//生成一个贴图，然后绘制它

sp<LayerBuffer::Buffer>LayerBuffer::BufferSource::getBuffer() const

    Mutex::Autolock_l(mBufferSourceLock);

    returnmBuffer;

从代码的分析来看，这种方式确实有问题。我在真实设备上测试的结果，也在一定程度上验证了这一点。通过修改LayerBuffer来解决这问题的难度比较大，是否可在读写具体缓存时加上同步控制呢（例如使用mBuffers[0]的时候调用一下lock，用完后调用unlock）？这样就不用修改LayerBuffer了。读者可再深入研究这个问题。